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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Sep. 30, 2012	Oct. 31, 2012
Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Entity Registrant Name	American Capital Agency Corp
Entity Central Index Key	0001423689
Entity Filer Category	Large Accelerated Filer
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		341,598,550
Trading Symbol	AGNC

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Assets:
Agency securities, at fair value	$ 88,020	$ 54,625
Agency securities transferred to consolidated variable interest entities, at fair value	1,620	58
U.S. Treasury securities, at fair value	0	101
Cash and cash equivalents	2,569	1,367
Restricted cash	369	336
Derivative assets, at fair value	292	82
Receivable for agency securities sold	2,326	443
Receivable under reverse repurchase agreements	6,712	763
Other assets	269	197
Total assets	102,177	57,972
Liabilities:
Repurchase agreements	79,254	47,681
Other debt	1,008	54
Payable for agency securities purchased	1,311	1,919
Derivative liabilities, at fair value	1,562	853
Dividend payable	430	314
Obligation to return securities borrowed under reverse repurchase agreements, at fair value	7,265	899
Accounts payable and other accrued liabilities	74	40
Total liabilities	90,904	51,760
Stockholders' equity:
Preferred stock	167	0
Common stock	3	2
Additional paid-in capital	9,536	5,937
Retained earnings (deficit)	(672)	(38)
Accumulated other comprehensive income	2,239	311
Total stockholders' equity	11,273	6,212
Total liabilities and stockholders' equity	$ 102,177	$ 57,972

Consolidated Balance Sheets (Parentheticals) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale Securities Pledged as Collateral	$ 83,600	$ 50,667
Assets Pledged included in Receivable for Securities Sold	1,466	$ 319
Debt Instrument, Fair Value Disclosure	$ 968
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	10.0	10.0
Preferred Stock, Shares Issued	6.9	0.0
Preferred Stock, Shares Outstanding	6.9	0.0
Pref'd Stock Liquidation Preference	$ 173	$ 0
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	600.0	300.0
Common Stock, Shares, Issued	341.6	224.1
Common Stock, Shares, Outstanding	341.6	224.1

Consolidated Statements Of Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest income:
Interest income	$ 520	$ 327	$ 1,538	$ 756
Interest expense	139	95	365	195
Net interest income	381	232	1,173	561
Other income, net:
Gain on sale of agency securities, net	210	263	843	361
(Loss) gain on derivative instruments and other securities, net	(460)	(222)	(1,442)	(310)
Total other income, net	(250)	41	(599)	51
Expenses:
Management fees	32	16	82	36
General and administrative expenses	8	6	22	13
Total expenses	40	22	104	49
Income before income tax	91	251	470	563
Income tax benefit, net	5	1	4	1
Net income	86	250	466	562
Dividend on preferred stock	3	0	6	0
Comprehensive income available to common shareholders	1,324	274	2,388	673
Net (loss) income (attributable) available to common shareholders	83	250	460	562
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	1,190	536	1,773	815
Unrealized (loss) gain on derivative instruments, net	51	(512)	155	(704)
Other comprehensive income (loss)	1,241	24	1,928	111
Comprehensive income	$ 1,327	$ 274	$ 2,394	$ 673
Weighted average number of common shares outstanding-basic and diluted	332.8	180.7	291.6	134.2
Net income per common share - basic and diluted	$ 0.25	$ 1.39	$ 1.58	$ 4.19
Comprehensive income per share - basic and diluted	3.98	1.52	8.19	5.01
Dividends declared per common share	$ 1.25	$ 1.40	$ 3.75	$ 4.20

Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Interest Rate Swap [Member]
Balance, value at Dec. 31, 2011	$ 6,212.0	$ 0.0	$ 2.0	$ 5,937.0	$ (38.0)	$ 311.0
Balance, Preferred Stock, shares at Dec. 31, 2011	0	0
Balance, Common Stock, shares at Dec. 31, 2011	224,100,000		224,100,000
Net income	$ 641.0				641.0
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	(106.0)					(106.0)
Unrealized (loss) gain on derivative instruments, net	52.0
Unrealized (loss) gain on derivative instruments, net \| Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member]							$ 52.0
Issuance of common stock, value	2,205.0		$ 1.0	2,204.0
Issuance of common stock, shares			75,900,000
Common dividends declared	286.0				(286.0)
Balance, value at Mar. 31, 2012	8,718.0	$ 0.0	$ 3.0	8,141.0	317.0	257.0
Balance, Preferred Stock, shares at Mar. 31, 2012		0
Balance, Common Stock, shares at Mar. 31, 2012			300,000,000
Balance, value at Dec. 31, 2011	$ 6,212.0	$ 0.0	$ 2.0	5,937.0	(38.0)	311.0
Balance, Preferred Stock, shares at Dec. 31, 2011	0	0
Balance, Common Stock, shares at Dec. 31, 2011	224,100,000		224,100,000
Net income	$ 466.0
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	1,773.0
Unrealized (loss) gain on derivative instruments, net	155.0
Balance, value at Sep. 30, 2012	$ 11,273.0	$ 167.0	$ 3.0	9,536.0	(672.0)	2,239.0
Balance, Preferred Stock, shares at Sep. 30, 2012	6,900,000	6,900,000
Balance, Common Stock, shares at Sep. 30, 2012	341,600,000		341,600,000
Other comprehensive income (loss):
Proceeds from Issuance of Preferred Stock and Preference Stock	$ 167.0
Balance, value at Mar. 31, 2012	8,718.0	$ 0.0	$ 3.0	8,141.0	317.0	257.0
Balance, Preferred Stock, shares at Mar. 31, 2012		0
Balance, Common Stock, shares at Mar. 31, 2012			300,000,000
Net income	(261.0)				(261.0)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	689.0					689.0
Unrealized (loss) gain on derivative instruments, net	52.0
Unrealized (loss) gain on derivative instruments, net \| Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member]							52.0
Issuance of common stock, value	155.0			155.0
Dividends, Preferred Stock	(3.0)
Issuance of common stock, shares			4,800,000
Common dividends declared	381.0				(381.0)
Balance, value at Jun. 30, 2012	9,136.0	$ 167.0	$ 3.0	8,296.0	(328.0)	998.0
Balance, Preferred Stock, shares at Jun. 30, 2012		6,900,000
Balance, Common Stock, shares at Jun. 30, 2012			304,800,000
Other comprehensive income (loss):
issuance of preferred stock	6.9
Proceeds from Issuance of Preferred Stock and Preference Stock	167.0
Net income	86.0				86.0
Unrealized gain (loss) on available-for-sale securities, net	1,190.0					1,190.0
Unrealized (loss) gain on derivative instruments, net	51.0
Unrealized (loss) gain on derivative instruments, net \| Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member]							$ 51.0
Issuance of common stock, value	1,240.0			1,240.0
Dividends, Preferred Stock	(3.0)
Issuance of common stock, shares			36,800,000
Common dividends declared	427.0				(427.0)
Balance, value at Sep. 30, 2012	$ 11,273.0	$ 167.0	$ 3.0	$ 9,536.0	$ (672.0)	$ 2,239.0
Balance, Preferred Stock, shares at Sep. 30, 2012	6,900,000	6,900,000
Balance, Common Stock, shares at Sep. 30, 2012	341,600,000		341,600,000

Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Operating activities:
Net income	$ 466	$ 562
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of agency securities premiums and discounts, net	515	240
Amortization of accumulated other comprehensive loss on interest rate swaps de-designated as qualifying hedges	155	0
Gain on sale of agency securities, net	(843)	(361)
Loss (gain) on derivative instruments and other securities, net	1,442	310
Increase in other assets	(79)	(91)
Accretion of discounts on other debt	2	0
Increase in accounts payable and other accrued liabilities	25	9
Net cash provided by operating activities	1,683	669
Investing activities:
Purchases of agency securities	(86,435)	(56,423)
Proceeds from sale of agency securities	44,218	24,351
Principal collections on agency securities	6,906	3,058
Purchases of U.S. Treasury securities	(2,444)	(4,059)
Proceeds from sale of U.S. Treasury securities	2,545	3,791
Proceeds from U.S. Treasury securities sold prior to purchase	29,698	12,054
Purchase of U.S. Treasury securities sold prior to purchase	(23,450)	(11,919)
Proceeds from reverse repurchase agreements	50,715	28,615
Payments made on reverse repurchase agreements	(56,661)	(28,842)
Net (payments) receipts on other derivative instruments not designated as qualifying hedges	(816)	(194)
Decrease in restricted cash	(33)	(298)
Net cash used in investing activities	(35,757)	(29,866)
Financing activities:
Proceeds from repurchase arrangements, net	310,225	247,495
Payments made on repurchase agreements	(278,652)	(220,333)
Proceeds from other debt	1,000	0
Repayments on other debt	(80)	(16)
Proceeds from Issuance of Preferred Stock and Preference Stock	167
Net proceeds from common stock issuances	3,600	3,268
Cash dividends paid	(984)	(406)
Net cash provided by financing activities	35,276	30,008
Net change in cash and cash equivalents	1,202	811
Cash and cash equivalents at beginning of period	1,367	173
Cash and cash equivalents at end of period	$ 2,569	$ 984

Unaudited Interim Consolidated Financial Statements	9 Months Ended
Unaudited Interim Consolidated Financial Statements	Sep. 30, 2012
Unaudited Interim Financials [Abstract]
Unaudited Interim Consolidated Financial Statements	Unaudited Interim Consolidated Financial Statements The interim consolidated financial statements of American Capital Agency Corp. (referred throughout this report as the “Company”, “we”, “us” and “our”) are prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and pursuant to the requirements for reporting on Form 10-Q and Article 10 of Regulation S-X. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period. Actual results could differ from those estimates. Our unaudited consolidated financial statements include the accounts of our wholly-owned taxable REIT subsidiary, American Capital Agency TRS, LLC, and variable interest entities for which the Company is the primary beneficiary. Significant intercompany accounts and transactions have been eliminated. In the opinion of management, all adjustments, consisting solely of normal recurring accruals, necessary for the fair presentation of financial statements for the interim period have been included. The current period’s results of operations are not necessarily indicative of results that ultimately may be achieved for the year.

- Definition

Disclosure of accounting policy regarding (1) the principles it follows in consolidating or combining the separate financial statements, including the principles followed in determining the inclusion or exclusion of subsidiaries or other entities in the consolidated or combined financial statements and (2) its treatment of interests (for example, common stock, a partnership interest or other means of exerting influence) in other entities, for example consolidation or use of the equity or cost methods of accounting. The accounting policy may also address the accounting treatment for intercompany accounts and transactions, noncontrolling interest, and the income statement treatment in consolidation for issuances of stock by a subsidiary.

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+ Details

Organization	9 Months Ended
Organization	Sep. 30, 2012
Organization [Abstract]
Organization	Organization We were organized in Delaware on January 7, 2008, and commenced operations on May 20, 2008 following the completion of our initial public offering (“IPO”). Our common stock is traded on The NASDAQ Global Select Market under the symbol “AGNC”. We operate so as to qualify to be taxed as a real estate investment trust (“REIT”) under the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”). Therefore, substantially all of our assets, other than our taxable REIT subsidiary ("TRS"), consist of qualified real estate assets (as defined under the Internal Revenue Code). As a REIT, we are required to distribute annually 90% of our taxable net income. As long as we qualify as a REIT, we will generally not be subject to U.S. federal or state corporate taxes on our taxable net income to the extent that we distribute all of our annual taxable net income to our stockholders. It is our intention to distribute 100% of our taxable income, after application of available tax attributes, within the limits prescribed by the Internal Revenue Code, which may extend into the subsequent taxable year. We are externally managed by American Capital AGNC Management, LLC (our “Manager”), an affiliate of American Capital, Ltd. (“American Capital”). We earn income primarily from investing on a leveraged basis in agency mortgage-backed securities ("agency MBS"). These investments consist of residential mortgage pass-through securities and collateralized mortgage obligations (“CMOs”) for which the principal and interest payments are guaranteed by government-sponsored entities, such as the Federal National Mortgage Association (“Fannie Mae”) and the Federal Home Loan Mortgage Corporation (“Freddie Mac”), or by a U.S. Government agency, such as the Government National Mortgage Association (“Ginnie Mae”) (collectively referred to as “GSEs”). We may also invest in agency debenture securities issued by Freddie Mac, Fannie Mae or the Federal Home Loan Bank ("FHLB"). We refer to agency MBS and agency debenture securities collectively as "investment securities" and we refer to the specific investment securities in which we invest as our "investment portfolio". Our principal objective is to preserve our net asset value (also referred to as "net book value", "NAV" and "stockholders' equity") while generating attractive risk-adjusted returns for distribution to our stockholders through regular quarterly dividends from the combination of our net interest income and net realized gains and losses on our investments and hedging activities. We fund our investments primarily through short-term borrowings structured as repurchase agreements.

- Definition

The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.

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+ Details

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2012
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Investment Securities ASC Topic 320, Investments—Debt and Equity Securities (“ASC 320”), requires that at the time of purchase, we designate a security as held-to-maturity, available-for-sale or trading, depending on our ability and intent to hold such security to maturity. Securities classified as trading and available-for-sale are reported at fair value, while securities classified as held-to-maturity are reported at amortized cost. We may, from time to time, sell any of our investment securities as part of our overall management of our investment portfolio. Accordingly, we typically designate our investment securities as available-for-sale. All securities classified as available-for-sale are reported at fair value, with unrealized gains and losses reported in other comprehensive income ("OCI") a separate component of stockholders’ equity. Upon the sale of a security, we determine the cost of the security and the amount of unrealized gains or losses to reclassify out of accumulated OCI into earnings based on the specific identification method. Interest-only securities and inverse interest-only securities (collectively referred to as “interest-only securities”) represent our right to receive a specified proportion of the contractual interest flows of specific agency CMO securities. Principal-only securities represent our right to receive the contractual principal flows of specific agency CMO securities. Interest-only and principal-only securities are measured at fair value through earnings in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income. Our investments in interest-only and principal-only securities are included in agency MBS securities, at fair value on the accompanying consolidated balance sheets. We estimate the fair value of our investment securities based on a market approach using Level 2 inputs from third-party pricing services and dealer quotes. The third-party pricing services use pricing models that incorporate such factors as coupons, primary and secondary mortgage rates, prepayment speeds, spread to the Treasury and interest rate swap curves, convexity, duration, periodic and life caps and credit enhancements. The dealer quotes incorporate common market pricing methods, including a spread measurement to the Treasury or interest rate swap curve as well as underlying characteristics of the particular security including coupon, periodic and life caps, rate reset period, issuer, additional credit support and expected life of the security. Refer to Note 7 for further discussion of fair value measurements. We evaluate securities for other-than-temporary impairment (“OTTI”) on at least a quarterly basis, and more frequently when economic or market conditions warrant such evaluation. The determination of whether a security is other-than-temporarily impaired involves judgments and assumptions based on subjective and objective factors. When an investment security is impaired, an OTTI is considered to have occurred if (i) we intend to sell the investment security (i.e. a decision has been made as the reporting date) or (ii) it is more likely than not that we will be required to sell the investment security before recovery of its amortized cost basis. If we intend to sell the security or if it is more likely than not that we will be required to sell the investment security before recovery of its amortized cost basis, the entire amount of the impairment loss, if any, is recognized in earnings as a realized loss and the cost basis of the security is adjusted to its fair value. We did not recognize any OTTI charges on any of our investment securities for the three and nine months ended September 30, 2012 and 2011. Interest Income Interest income is accrued based on the outstanding principal amount of the investment securities and their contractual terms. Premiums and discounts associated with the purchase of investment securities are amortized or accreted into interest income over the projected lives of the securities, including contractual payments and estimated prepayments using the interest method in accordance with ASC Subtopic 310-20, Receivables—Nonrefundable Fees and Other Costs (“ASC 310-20”). We estimate long-term prepayment speeds of our agency securities using a third-party service and market data. The third-party service estimates prepayment speeds using models that incorporate the forward yield curve, current mortgage rates, current mortgage rates of the outstanding loans, loan age, volatility and other factors. We review the prepayment speeds estimated by the third-party service and compare the results to market consensus prepayment speeds, if available. We also consider historical prepayment speeds and current market conditions to validate the reasonableness of the prepayment speeds estimated by the third-party service and, based on our Manager’s judgment, we may make adjustments to their estimates. Actual and anticipated prepayment experience is reviewed quarterly and effective yields are recalculated when differences arise between (i) our previously estimated future prepayments and (ii) actual prepayments to date plus current estimated future prepayments. If the actual and estimated future prepayment experience differs from our prior estimate of prepayments, we are required to record an adjustment in the current period to the amortization or accretion of premiums and discounts for the cumulative difference in the effective yield through the reporting date. The yield on our adjustable rate securities further assumes that the securities reset at a rate equal to the underlying index rate in effect as of the date we acquired the security plus the stated margin. Derivative and other Hedging Instruments We use a variety of derivative instruments to economically hedge a portion of our exposure to market risks, including interest rate and prepayment risk. The objective of our risk management strategy is to reduce fluctuations in net book value over a range of interest rate scenarios. In particular, we attempt to mitigate the risk of the cost of our variable rate liabilities increasing during a period of rising interest rates. The principal instruments that we use are interest rate swaps and options to enter into interest rate swaps (“interest rate swaptions”). We also purchase or sell to-be-announced agency MBS forward contracts (“TBAs”), specified agency MBS on a forward basis, U.S. Treasury securities and U.S. Treasury futures contracts. We may also purchase or write put or call options on TBA securities and invest in other types of mortgage derivatives, such as interest-only securities, and synthetic total return swaps, such as the Markit IOS Synthetic Total Return Swap Index (“Markit IOS Index”). We account for derivative instruments in accordance with ASC Topic 815, Derivatives and Hedging (“ASC 815”). ASC 815 requires an entity to recognize all derivatives as either assets or liabilities in the balance sheet and to measure those instruments at fair value. Hedging instruments that are not derivatives under ASC 815 are accounted for as securities in accordance with ASC 320. The accounting for changes in the fair value of derivative instruments depends on whether the instruments are designated and qualify as part of a hedging relationship pursuant to ASC 815. Changes in fair value related to derivatives not in hedge designated relationships are recorded in gain (loss) on derivative instruments and other securities, net; whereas changes in fair value related to derivatives in hedge designated relationships are initially recorded in OCI and later reclassified to income at the time that the hedged transactions affect earnings. Any portion of the changes in fair value due to hedge ineffectiveness is immediately recognized in gain (loss) on derivative instruments and other securities, net. Our derivative agreements and repurchase agreements generally contain provisions that allow for netting or setting off receivables and payables with each counterparty. We report amounts in our consolidated balance sheets on a gross basis without regard for such rights of offset or master netting arrangements. Derivatives in a gain position are reported as derivative assets at fair value and derivatives in a loss position are reported as derivative liabilities at fair value in our consolidated balance sheets. In our consolidated statements of cash flows, cash receipts and payments related to derivative instruments are classified according to the underlying nature or purpose of the derivative transaction, generally in the operating section for derivatives designated in hedging relationships and the investing section for derivatives not designated in hedging relationships. The use of derivatives creates exposure to credit risk relating to potential losses that could be recognized in the event that the counterparties to these instruments fail to perform their obligations under the contracts. We attempt to minimize this risk by limiting our counterparties to major financial institutions with acceptable credit ratings, monitoring positions with individual counterparties and adjusting posted collateral as required. Discontinuation of hedge accounting for interest rate swap agreements Prior to the third quarter of 2011, we entered into interest rate swap agreements typically with the intention of qualifying for hedge accounting under ASC 815. However, as of September 30, 2011, we elected to discontinue hedge accounting for our interest rate swaps. Our net asset value was not impacted by our election to discontinue hedge accounting since our net asset value is the same irrespective of whether we apply hedge accounting. Upon discontinuation of hedge accounting, the net deferred loss related to our de-designated interest rate swaps remained in accumulated OCI and is being reclassified from accumulated OCI into interest expense on a straight-line basis over the remaining term of each interest rate swap. Although the reclassification of accumulated OCI into interest expense is similar to as if the interest rate swaps had not been de-designated, the actual net periodic interest costs associated with our de-designated interest rates swaps may be more or less than amounts reclassified into interest expense. The difference, as well as net periodic interest costs on interest rate swaps that were never in a hedge designation, along with subsequent changes in the fair value of our interest rates swaps, is reported in our consolidated statement of comprehensive income in gain (loss) on derivative instruments and other securities, net. Interest rate swap agreements We use interest rate swaps to economically hedge the variable cash flows associated with borrowings made under our repurchase agreement facilities. Under our interest rate swap agreements, we typically pay a fixed rate and receive a floating rate based on one or three-month LIBOR ("payer swap") with terms up to 10 years, which has the effect of modifying the repricing characteristics of our repurchase agreements and cash flows on such liabilities. We estimate the fair value of interest rate swaps using a third-party pricing model. The third-party pricing model incorporates such factors as the LIBOR curve and the pay rate on the interest rate swaps. We also incorporate both our own and our counterparties’ nonperformance risk in estimating the fair value of our interest rate swaps. In considering the effect of nonperformance risk, we consider the impact of netting and credit enhancements, such as collateral postings and guarantees, and have concluded that our own and our counterparty risk is not significant to the overall valuation of these agreements. Interest rate swaptions We purchase interest rate swaptions to help mitigate the potential impact of increases or decreases in interest rates on the performance of our investment portfolio (referred to as “convexity risk”). The interest rate swaptions provide us the option to enter into an interest rate swap agreement for a predetermined notional amount, stated term and pay and receive interest rates in the future. Our swaption agreements typically provide us the option to enter into a pay fixed rate interest rate swap, which we refer as “payer swaptions”. We may also enter into swaption agreements that provide us the option to enter into a receive fixed interest rate swap, which we refer to as "receiver swaptions". The premium paid for interest rate swaptions is reported as an asset in our consolidated balance sheets. The premium is valued at an amount equal to the fair value of the swaption that would have the effect of closing the position adjusted for nonperformance risk, if any. The difference between the premium and the fair value of the swaption is reported in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income. If a swaption expires unexercised, the loss on the swaption would be equal to the premium paid. If we sell or exercise a swaption, the realized gain or loss on the swaption would be equal to the difference between the cash or the fair value of the underlying interest rate swap received and the premium paid. We estimate the fair value of interest rate swaptions using a third-party pricing model based on the fair value of the future interest rate swap that we have the option to enter into as well as the remaining length of time that we have to exercise the option, adjusted for non-performance risk, if any. TBA securities A TBA security is a forward contract for the purchase ("long position") or sale ("short position") of agency MBS at a predetermined price, face amount, issuer, coupon and stated maturity on an agreed-upon future date. The specific agency MBS delivered into the contract upon the settlement date, published each month by the Securities Industry and Financial Markets Association, are not known at the time of the transaction. The difference between the contract price and the fair value of the TBA security is reported in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income. Upon settlement of the TBA contract, the realized gain or loss on the TBA contract is equal to the difference between the fair value of the underlying agency MBS physically received/delivered and the contract price, or if cash settled, is equal to the net cash amount paid or received. We estimate the fair value of TBA securities based on similar methods used to value our agency MBS securities. Forward commitments to purchase or sell specified agency MBS We enter into forward commitments to purchase or sell specified agency MBS from time to time as a means of acquiring assets or as a hedge against short-term changes in interest rates. We account for contracts for the purchase or sale of specified agency MBS securities as derivatives if the delivery of the specified agency MBS and settlement extends beyond the shortest period possible for that type of security. Realized and unrealized gains and losses associated with forward commitments accounted for as derivatives are recognized in our consolidated statements of comprehensive income in gain (loss) on derivative instruments and other securities, net. We estimate the fair value of forward commitments to purchase or sell specified agency MBS based on similar methods used to value agency MBS, as well as the remaining length of time of the forward commitment. U.S. Treasury securities We purchase or sell short U.S. Treasury securities and U.S. Treasury futures contracts to help mitigate the potential impact of changes in interest rates on the performance of our portfolio. We borrow securities to cover short sales of U.S. Treasury securities under reverse repurchase agreements. We account for these as securities borrowing transactions and recognize an obligation to return the borrowed securities at fair value on the balance sheet based on the value of the underlying borrowed securities as of the reporting date. Gains and losses associated with purchases and short sales of U.S. Treasury securities are recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income. Total return swaps We enter into total return swaps to obtain exposure to a security or market sector without owning such security or investing directly in that market sector. Total return swaps are agreements in which there is an exchange of cash flows whereby one party commits to make payments based on the total return (coupon plus the mark-to-market movement) of an underlying instrument or index in exchange for fixed or floating rate interest payments. To the extent the total return of the instrument or index underlying the transaction exceeds or falls short of the offsetting interest rate obligation, we will receive a payment from or make a payment to the counterparty. The primary total return swap index in which we invest is the Markit IOS Index. Total return swaps based on the Markit IOS Index are intended to synthetically replicate the performance of interest-only securities. We determine the fair value of our total return swaps based on published index prices. Gains and losses associated with changes in market value of the underlying index and coupon interest are recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income. Variable Interest Entities ASC Topic 810, Consolidation (“ASC 810”), requires an enterprise to consolidate a variable interest entity ("VIE") if it is deemed the primary beneficiary of the VIE. Further, ASC 810 requires a qualitative assessment to determine the primary beneficiary of a VIE and ongoing assessments of whether an enterprise is the primary beneficiary of a VIE as well as additional disclosures for entities that have variable interests in VIEs. We have entered into transactions involving CMO trusts (e.g. a VIE) whereby, in each case, we transferred agency MBS to an investment bank in exchange for cash proceeds and at the same time entered into a commitment with the same investment bank to purchase to-be-issued securities collateralized by the agency MBS transferred, which resulted in our consolidation of the CMO trusts. We will consolidate a CMO trust if we are the CMO trust’s primary beneficiary; that is, if we have a variable interest that provides us with a controlling financial interest in the CMO trust. An entity is deemed to have a controlling financial interest if the entity has the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance and the obligation to absorb losses of or right to receive benefits from the VIE that could potentially be significant to the VIE. As part of the qualitative assessment in determining if we have a controlling financial interest, we evaluate whether we control the selection of financial assets transferred to the CMO trust. Agency MBS transferred to consolidated VIEs are reported on our consolidated balance sheets in agency securities transferred to consolidated variable interest entities, at fair value and can only be used to settle the obligations of each respective VIE. We report debt issued in connection with the CMO trusts on our consolidated balance sheets in debt of consolidated VIEs, at fair value, which represents tranches within the trusts sold to third-parties and excludes tranches acquired by us that eliminate in consolidation. The third-party beneficial interest holders in the VIEs have no recourse against our general credit. For transactions entered into subsequent to December 31, 2011, we have elected the option to account for the consolidated debt at fair value, with changes in fair value reflected in earnings during the period in which they occur. We believe this election more appropriately reflects our financial position as both the consolidated assets and consolidated debt are presented in a consistent manner on our consolidated balance sheets. We estimate the fair value of the consolidated debt based on a market approach using Level 2 inputs from third-party pricing services and dealer quotes. Recent Accounting Pronouncements In December 2011, the FASB issued ASU No. 2011-11, Balance Sheet (Topic 210): Disclosures about Offsetting Assets and Liabilities (“ASU 2011-11”). The update requires new disclosures about balance sheet offsetting and related arrangements. For derivatives and financial assets and liabilities, the amendments require disclosure of gross asset and liability amounts, amounts offset on the balance sheet, and amounts subject to the offsetting requirements but not offset on the balance sheet. The guidance is effective January 1, 2013 and is to be applied retrospectively. This guidance does not amend the existing guidance on when it is appropriate to offset. As a result, we do not expect this guidance to have a material effect on our financial statements. Reclassifications Certain prior period amounts in the consolidated financial statements have been reclassified to conform to the current period presentation.

Investment Securities

9 Months Ended

Sep. 30, 2012

Available-for-sale Securities [Abstract]

Investment Securities

As of September 30, 2012, we had agency MBS at fair value of $89.6 billion, with a total cost basis of $86.9 billion. The net unamortized premium balance on our investment portfolio as of September 30, 2012 was $4.4 billion, including interest-only and principal-only strips. The following tables summarize our investments in agency MBS as of September 30, 2012 (dollars in millions):



	September 30, 2012
Agency MBS	Fannie Mae			Freddie Mac			Ginnie Mae			Total
Available-for-sale agency MBS:
Agency MBS, par	$	64,352		$	17,512		$	260		$	82,124
Unamortized premium	3,319			827			12			4,158
Amortized cost	67,671			18,339			272			86,282
Gross unrealized gains	2,161			617			6			2,784
Gross unrealized losses	(1		)	—			—			(1		)
Total available-for-sale agency MBS, at fair value	69,831			18,956			278			89,065
Agency MBS remeasured at fair value through earnings:
Interest-only and principal-only strips, amortized cost ⁽¹⁾	508			60			—			568
Gross unrealized gains	30			1			—			31
Gross unrealized losses	(12		)	(12		)	—			(24		)
Total agency MBS remeasured at fair value through earnings	526			49			—			575
Total agency MBS, at fair value	$	70,357		$	19,005		$	278		$	89,640
Weighted average coupon as of September 30, 2012⁽²⁾	3.74		%	3.88		%	3.78		%	3.77		%
Weighted average yield as of September 30, 2012⁽³⁾	2.56		%	2.82		%	1.60		%	2.61		%
Weighted average yield for the three months ended September 30, 2012⁽³⁾	2.53		%	2.62		%	1.54		%	2.55		%
Weighted average yield for the nine months ended September 30, 2012⁽³⁾	2.82		%	2.85		%	1.64		%	2.82		%

________________________

Interest-only agency MBS strips represent the right to receive a specified portion of the contractual interest flows of the underlying unamortized principal balance (“UPB” or “par value”) of specific agency CMO securities. Principal-only agency MBS strips represent the right to receive contractual principal flows of the UPB of specific agency CMO securities. The UPB of our interest-only agency MBS strips was $1.8 billion and the weighted average contractual interest we are entitled to receive was 5.70% of this amount as of September 30, 2012. The par value of our principal-only agency MBS strips was $309 million as of September 30, 2012.


2.	The weighted average coupon includes the interest cash flows from our interest-only agency MBS strips taken together with the interest cash flows from our fixed-rate, adjustable-rate and CMO agency MBS as a percentage of the par value of our agency MBS (excluding the UPB of our interest-only securities) as of September 30, 2012.


3.	Incorporates a weighted average future constant prepayment rate assumption of 14% based on forward rates as of September 30, 2012 and a weighted average reset rate for adjustable rate securities of 2.67%, which is equal to a weighted average underlying index rate of 0.96% based on the current spot rate in effect as of the date we acquired the securities and a weighted average margin of 1.71%.



	September 30, 2012
Agency MBS	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Fixed-Rate	$	85,136	$	2,747	$	(1	)	$	87,882
Adjustable-Rate	960		32		—			992
CMO	186		5		—			191
Interest-only and principal-only strips	568		31		(24		)	575
Total agency MBS	$	86,850	$	2,815	$	(25	)	$	89,640

As of December 31, 2011, we had agency MBS at fair value of $54.7 billion, with a total cost basis of $53.7 billion. The net unamortized premium balance on our investment portfolio as of December 31, 2011 was $2.4 billion, including interest-only and principal-only strips. The following tables summarize our investments in agency MBS as of December 31, 2011 (dollars in millions):



	December 31, 2011
Agency MBS	Fannie Mae			Freddie Mac			Ginnie Mae			Total
Available-for-sale agency MBS:
Agency MBS, par	$	37,232		$	13,736		$	258		$	51,226
Unamortized premium	1,659			606			12			2,277
Amortized cost	38,891			14,342			270			53,503
Gross unrealized gains	680			324			3			1,007
Gross unrealized losses	(4		)	(2		)	—			(6		)
Available-for-sale agency MBS, at fair value	39,567			14,664			273			54,504
Agency MBS remeasured at fair value through earnings:
Interest-only and principal-only strips, amortized cost ⁽¹⁾	124			67			—			191
Gross unrealized gains	6			3			—			9
Gross unrealized losses	(8		)	(13		)	—			(21		)
Agency MBS remeasured at fair value through earnings	122			57			—			179
Total agency MBS, at fair value	$	39,689		$	14,721		$	273		$	54,683
Weighted average coupon as of December 31, 2011 ⁽²⁾	4.18		%	4.39		%	3.74		%	4.23		%
Weighted average yield as of December 31, 2011 ⁽³⁾	3.03		%	3.20		%	1.71		%	3.07		%
Weighted average yield for the year ended December 31, 2011 ⁽³⁾	3.19		%	3.20		%	2.05		%	3.19		%

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1.	The UPB of our interest-only securities was $1.1 billion and the weighted average contractual interest we are entitled to receive was 5.52% of this amount as of December 31, 2011. The par value of our principal-only agency MBS strips was $40 million as of December 31, 2011.


2.	The weighted average coupon includes the interest cash flows from our interest-only securities taken together with the interest cash flows from our fixed-rate, adjustable-rate and CMO securities as a percentage of the par value of our agency securities (excluding the UPB of our interest-only securities) as of December 31, 2011.


3.	Incorporates a weighted average future constant prepayment rate assumption of 14% based on forward rates as of December 31, 2011 and a weighted average reset rate for adjustable rate securities of 2.71%, which is equal to a weighted average underlying index rate of 0.94% based on the current spot rate in effect as of the date we acquired the securities and a weighted average margin of 1.77%.



	December 31, 2011
Agency MBS	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Fixed-Rate	$	50,535	$	952	$	(4	)	$	51,483
Adjustable-Rate	2,725		51		(2		)	2,774
CMO	243		4		—			247
Interest-only strips	191		9		(21		)	179
Total agency MBS	$	53,694	$	1,016	$	(27	)	$	54,683

As of September 30, 2012 and December 31, 2011, we did not have investments in agency debenture securities.

The actual maturities of our agency MBS securities are generally shorter than the stated contractual maturities. Actual maturities are affected by the contractual lives of the underlying mortgages, periodic contractual principal payments and principal prepayments. As of September 30, 2012 and December 31, 2011, our weighted average expected constant prepayment rate (“CPR”) over the remaining life of our aggregate agency MBS portfolio was 14%. Our estimates differ materially for different types of securities and thus individual holdings have a wide range of projected CPRs. We estimate long-term prepayment assumptions for different securities using a third-party service and market data. The third-party service estimates prepayment speeds using models that incorporate the forward yield curve, current mortgage rates, mortgage rates of the outstanding loans, loan age, volatility and other factors. We review the prepayment speeds estimated by the third-party service and compare the results to market consensus prepayment speeds, if available. We also consider historical prepayment speeds and current market conditions to validate reasonableness. As market conditions may change rapidly, we may make adjustments for different securities based on our Manager's judgement. Various market participants could use materially different assumptions.

The following table summarizes our agency MBS classified as available-for-sale as of September 30, 2012 and December 31, 2011 according to their estimated weighted average life classification (dollars in millions):



	September 30, 2012						December 31, 2011
Estimated Weighted Average Life of Agency MBS Classified as Available-for-Sale	Fair Value		Amortized Cost		Weighted Average Coupon		Fair Value		Amortized Cost		Weighted Average Coupon
Less than or equal to 1 year	$	—	$	—	—	%	$	214	$	210	4.61	%
Greater than 1 year and less than/equal to 3 years	9,902		9,656		3.17	%	3,392		3,338		4.38	%
Greater than 3 years and less than/equal to 5 years	39,737		38,442		3.66	%	26,168		25,616		3.99	%
Greater than 5 years and less than/equal to 10 years	38,832		37,600		3.80	%	24,710		24,320		4.19	%
Greater than 10 years	594		584		3.55	%	20		19		5.02	%
Total	$	89,065	$	86,282	3.66	%	$	54,504	$	53,503	4.11	%

The weighted average life of our interest-only agency MBS strips was 4.8 and 3.0 years as of September 30, 2012 and December 31, 2011, respectively. The weighted average life of our principal-only agency MBS strips was 5.6 and 2.6 years as of September 30, 2012 and December 31, 2011, respectively.

Our agency securities classified as available-for-sale are reported at fair value, with unrealized gains and losses excluded from earnings and reported in OCI, a component of stockholders’ equity. The following table summarizes changes in accumulated OCI for our available-for-sale securities for the three and nine months ended September 30, 2012 and 2011 (in millions):



Agency Securities Classified as Available-for-Sale	Beginning OCI Balance			Unrealized Gains and (Losses), Net	Reversal of Prior Period Unrealized (Gains) and Losses, Net on Realization		Ending OCI Balance
Three months ended September 30, 2012	$	1,585		1,400	(210	)	$	2,775
Three months ended September 30, 2011	$	251		802	(266	)	$	787
Nine months ended September 30, 2012	$	1,002		2,616	(843	)	$	2,775
Nine months ended September 30, 2011	$	(28	)	1,178	(363	)	$	787

The following table presents the gross unrealized loss and fair values of our available-for-sale agency securities by length of time that such securities have been in a continuous unrealized loss position as of September 30, 2012 and December 31, 2011 (in millions):



	Unrealized Loss Position For
	Less than 12 Months					12 Months or More				Total
Agency Securities Classified as Available-for-Sale	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		Unrealized Loss		Estimated Fair Value		Unrealized Loss
September 30, 2012	$	436	$	(1	)	$	—	$	—	$	436	$	(1	)
December 31, 2011	$	1,135	$	(6	)	$	—	$	—	$	1,135	$	(6	)

As of September 30, 2012, we did not intend to sell any of these agency securities and we do not believe it is more likely than not we will be required to sell the agency securities before recovery of their amortized cost basis. The unrealized losses on these agency securities are not due to credit losses given the government-sponsored entity or government guarantees, but are rather due to changes in interest rates and prepayment expectations.

Gains and Losses

The following table is a summary of our net gain from the sale of agency MBS for the three and nine months ended September 30, 2012 and 2011 (in millions):



	Three Months Ended						Nine Months Ended
Agency MBS	September 30, 2012			September 30, 2011			September 30, 2012			September 30, 2011
Agency MBS sold, at cost	$	(10,172	)	$	(14,046	)	$	(45,258	)	$	(26,429	)
Proceeds from agency MBS sold ⁽¹⁾	10,382			14,309			46,101			26,790
Net gains on sale of agency MBS	$	210		$	263		$	843		$	361

Gross gains on sale of agency MBS	$	210		$	268		$	855		$	377
Gross losses on sale of agency MBS	—			(5		)	(12		)	(16		)
Net gains on sale of agency MBS	$	210		$	263		$	843		$	361

________________________


1.	Proceeds include cash received during the period, plus receivable for agency MBS sold during the period as of period end.

For the three and nine months ended September 30, 2012, we recognized an unrealized gain of $20 million and $19 million, respectively, and for the three and nine months ended September 30, 2011, we recognized an unrealized gain of $28 million and $24 million, respectively, in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income for the change in value of investments in interest-only and principal-only agency MBS strips, net of prior period reversals. For the three and nine months ended September 30, 2012, we recognized no realized gain or loss, and for the three and nine months ended September 30, 2011, we recognized a realized loss of $3 million in gain on sale of agency securities, net, in our consolidated statements of operations and comprehensive income for the sales of interest-only and principal-only securities.

Pledged Assets

The following tables summarize our assets pledged as collateral under repurchase agreements, debt of consolidated VIEs, derivative agreements and prime broker agreements by type, including securities pledged related to securities sold but not yet settled, as of September 30, 2012 and December 31, 2011 (in millions):



	September 30, 2012
Assets Pledged	Repurchase Agreements		Debt of Consolidated VIEs		Derivative Agreements		Prime Broker Agreements		Total
Agency MBS - fair value	$	83,654	$	1,620	$	1,255	$	157	$	86,686
Accrued interest on pledged securities	234		5		4		—		243
Restricted cash	—		—		369		—		369
Total	$	83,888	$	1,625	$	1,628	$	157	$	87,298



	December 31, 2011
Assets Pledged	Repurchase Agreements		Debt of Consolidated VIEs		Derivative Agreements		Prime Broker Agreements		Total
Agency MBS - fair value	$	50,255	$	58	$	644	$	87	$	51,044
U.S. Treasury securities - fair value	101		—		—		—		101
Accrued interest on pledged securities	161		—		2		—		163
Restricted cash	—		—		336		—		336
Total	$	50,517	$	58	$	982	$	87	$	51,644

The following table summarizes our securities pledged as collateral under repurchase agreements and debt of consolidated VIEs by remaining maturity, including securities pledged related to sold but not yet settled securities, as of September 30, 2012 and December 31, 2011 (dollars in millions):



	September 30, 2012						December 31, 2011
Securities Pledged by Remaining Maturity of Repurchase Agreements and Debt of Consolidated VIEs	Fair Value of Pledged Securities		Amortized Cost of Pledged Securities		Accrued Interest on Pledged Securities		Fair Value of Pledged Securities		Amortized Cost of Pledged Securities		Accrued Interest on Pledged Securities
Agency MBS:
Less than 30 days	$	30,861	$	29,867	$	86	$	19,772	$	19,361	$	63
31 - 59 days	17,739		17,134		51		16,964		16,648		55
60 - 90 days	17,822		17,242		50		8,337		8,179		26
Greater than 90 days	18,852		18,348		52		5,240		5,154		17
Total agency MBS	85,274		82,591		239		50,313		49,342		161
U.S. Treasury securities:
1 day	—		—		—		101		101		—
Total securities	$	85,274	$	82,591	$	239	$	50,414	$	49,443	$	161

As of September 30, 2012 and December 31, 2011, none of our repurchase agreement borrowings backed by agency MBS were due on demand or mature overnight.

Securitizations

All of our CMO securities are backed by fixed or adjustable-rate agency MBS. Fannie Mae or Freddie Mac guarantees the payment of interest and principal and acts as the trustee and administrator of their respective securitization trusts. Accordingly, we are not required to provide the beneficial interest holders of the CMO securities any financial or other support. Our maximum exposure to loss related to our involvement with CMO trusts is the fair value of the CMO securities and interest-only and principal-only securities held by us, less principal amounts guaranteed by Fannie Mae and Freddie Mac.

As of September 30, 2012 and December 31, 2011, the fair value of all of our CMO securities, interest-only securities and principal-only securities, excluding the consolidated CMO trusts discussed below, was $766 million and $426 million, respectively, or $1.4 billion and $429 million, respectively, including the net asset value of the consolidated CMO trusts discussed below. Our maximum exposure to loss related to our CMO securities and interest-only and principal-only securities, including the consolidated CMO trust, was $375 million and $155 million as of September 30, 2012 and December 31, 2011, respectively.

We have consolidated CMO trusts for which we have determined we are the primary beneficiary of the trusts. In connection with the consolidated trusts, as of September 30, 2012 and December 31, 2011, we recognized agency securities with a total fair value of $1.6 billion and $58 million, respectively, and a principal balance of $1.5 billion and $55 million, respectively, and debt with a carrying value of $1.0 billion and $54 million, respectively, in our accompanying consolidated balance sheets. The total fair value of debt for which we have elected the option to account for at fair value was $968 million as of September 30, 2012, with a principal balance $939 million (or $936 million, net of discounts). For the three and nine months ended September 30, 2012, we recognized an unrealized loss of $24 million and $32 million in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income for the change in value of debt of our consolidated VIEs. Our involvement with the consolidated trusts is limited to the agency securities transferred to the trusts and the CMO securities subsequently held by us. There are no arrangements that could require us to provide financial support to the trusts.

Repurchase Agreements And Other Debt

9 Months Ended

Sep. 30, 2012

Disclosure of Repurchase Agreements [Abstract]

Repurchase Agreements And Other Debt

Repurchase Agreements and Other Debt

We pledge certain of our agency securities as collateral under repurchase arrangements with financial institutions, the terms and conditions of which are negotiated on a transaction-by-transaction basis. Interest rates on these borrowings are generally based on LIBOR plus or minus a margin and amounts available to be borrowed are dependent upon the fair value of the securities pledged as collateral, which fluctuates with changes in interest rates, type of security and liquidity conditions within the banking, mortgage finance and real estate industries. In response to declines in fair value of pledged securities, lenders may require us to post additional collateral or pay down borrowings to re-establish agreed upon collateral requirements, referred to as margin calls. As of September 30, 2012 and December 31, 2011, we have met all margin call requirements.

The following table summarizes our borrowings under repurchase arrangements and weighted average interest rates classified by original maturities as of September 30, 2012 and December 31, 2011 (dollars in millions):



	September 30, 2012					December 31, 2011
Original Maturity	Repurchase Agreements		Weighted Average Interest Rate		Weighted Average Days to Maturity	Repurchase Agreements		Weighted Average Interest Rate		Weighted Average Days to Maturity
Agency MBS:
1 month or less	$	4,724	0.43	%	12	$	2,558	0.43	%	10
1-3 months	31,253		0.43	%	37	24,518		0.39	%	32
4-6 months	25,571		0.45	%	72	16,475		0.37	%	53
7-9 months	8,641		0.49	%	92	2,423		0.45	%	141
10-12 months	7,547		0.57	%	266	1,006		0.53	%	244
13-24 months	693		0.67	%	613	600		0.51	%	268
25-36 months	825		0.72	%	992	—		—		—
Total agency MBS	79,254		0.46	%	89	47,580		0.40	%	51
U.S. Treasury securities:
1 day	—		—		—	101		0.40	%	1
Total / Weighted Average	$	79,254	0.46	%	89	$	47,681	0.40	%	51

As of September 30, 2012 and December 31, 2011, we did not have an amount at risk with any repurchase agreement counterparty greater than 4% of our stockholders’ equity.

As of September 30, 2012 and December 31, 2011, we had other debt consisting of debt of consolidated VIEs outstanding with a carrying value of $1.0 billion and $54 million, respectively, and a principal balance of $979 million (or $976 million, net of original issue discounts) and $54 million, respectively. Debt of consolidated VIEs consists of variable rate debt outstanding in connection with the consolidation of structured transactions for which we are the primary beneficiary of in our accompanying financial statements. As of September 30, 2012, debt of consolidated VIEs carried a weighted average interest rate of LIBOR plus 42 basis points. The actual maturities of debt of consolidated VIEs are generally shorter than the stated contractual maturities. The actual maturities are affected by the contractual lives of the underlying agency MBS securitizing the debt of consolidated VIEs and periodic principal prepayments of such underlying securities. The estimated weighted average life of debt of consolidated VIEs as of September 30, 2012 was 3.8 years.

Derivative and Other Hedging Instruments

9 Months Ended

Sep. 30, 2012

Derivative Asset, Fair Value, Net [Abstract]

Derivative and Other Hedging Instruments

In connection with our risk management strategy, we hedge a portion of our interest rate risk by entering into derivative and other hedging instrument contracts. We may enter into agreements for interest rate swaps, interest rate swaptions, interest rate cap or floor contracts and futures or forward contracts. We may also purchase or short TBA and U.S. Treasury securities, purchase or write put or call options on TBA securities or we may invest in other types of mortgage derivative securities, such as interest-only securities, and synthetic total return swaps, such as the Markit IOS Index. Our risk management strategy attempts to manage the overall risk of the portfolio, reduce fluctuations in book value and generate additional income distributable to stockholders. For additional information regarding our derivative instruments and our overall risk management strategy, please refer to the discussion of derivative and other hedging instruments in Note 3.

As of September 30, 2012 and December 31, 2011, our derivative and other hedging instruments were comprised primarily of interest rate swaps, which have the effect of economically modifying the repricing characteristics of our repurchase agreements and cash flows on such liabilities. Our interest rate swaps are used to manage the interest rate risk created by our variable rate short-term repurchase agreements. Under our interest rate swaps, we typically pay a fixed-rate and receive a floating rate based on one-month LIBOR with terms up to 10 years.

Derivative and other hedging instruments entered into in addition to interest rate swap agreements are intended to supplement our use of interest rate swaps and we do not currently expect our use of these instruments to be the primary protection against interest rate risk for our portfolio. These instruments are accounted for as derivatives, but are not generally designated as hedges under ASC 815, or as other securities, with any changes in the fair values of the contracts prior to their settlement date included in earnings in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income. We do not use derivative or other hedging instruments for speculative purposes.

Derivatives Designated as Hedging Instruments

Prior to September 30, 2011, our interest rate swaps were typically designated as cash flow hedges under ASC 815; however, as of September 30, 2011, we elected to discontinue hedge accounting for our interest rate swaps in order to increase our funding flexibility. For further information regarding our discontinuation of hedge accounting please refer to Note 3.

For the three and nine months ended September 30, 2012, we reclassified $51 million and $155 million, respectively, of net deferred losses from accumulated OCI into interest expense related to our de-designated interest rate swaps and recognized an equal, but offsetting, amount in other comprehensive income. Our total net periodic interest costs on our swap portfolio was $125 million and $330 million for the three and nine months ended September 30, 2012, respectively. The difference of $74 million and $175 million for the three and nine months ended September 30, 2012, respectively, are reported in our accompanying consolidated statement of comprehensive income in gain (loss) on derivative instruments and other securities, net. As of September 30, 2012, the net deferred loss in accumulated OCI related to de-designated interest rate swaps was $536 million and the weighted average remaining contractual term was 2.5 years. The net deferred loss expected to be reclassified from OCI into interest expense over the next twelve months is $194 million.

The following tables summarize information about our outstanding interest rate swaps designated as hedging instruments under ASC 815 and their effect on our consolidated statement of comprehensive income for the three and nine months ended September 30, 2011 (dollars in millions).



Interest Rate Swaps Designated as Hedging Instruments	Beginning Notional Amount		Additions	Expirations / Terminations		Hedge De-Designations		Ending Notional Amount
Three months ended September 30, 2011	$	22,000	2,100	(200	)	(23,900	)	$	—
Nine months ended September 30, 2011	$	6,450	17,900	(450	)	(23,900	)	$	—



Interest Rate Swaps Designated as Hedging Instruments:	Amount of Gain or (Loss) Recognized in OCI (Effective Portion)			Location of Gain or (Loss) Reclassified from OCI into Earnings (Effective Portion)	Amount of (Gain) or Loss Reclassified from OCI into Earnings (Effective Portion)		Location of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)	Amount of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Three Months Ended September 30, 2011	$	(512	)	Interest expense	(71	)	Gain (loss) on derivative instruments and other securities, net	$	(1	)
Nine Months Ended September 30, 2011	$	(707	)	Interest expense	(140	)	Gain (loss) on derivative instruments and other securities, net	$	(2	)

During the nine months ended September 30, 2011, we also held forward contracts to purchase TBA and specified agency securities that were designated as cash flow hedges pursuant to ASC 815. The following tables summarize information about these securities and their effect on our consolidated statement of comprehensive income for the nine months ended September 30, 2011 (dollars in millions). We did not designate any such agreements as cash flow hedges during the three months ended September 30, 2011 and the three and nine months ended September 30, 2012.



Purchases of TBAs and Forward Settling Agency Securities Designated as Hedging Instruments	Beginning Notional Amount		Additions		Settlement / Expirations			Ending Notional Amount		Fair Value as of Period End		Average Maturity as of Period End (Months)
Nine Months Ended September 30, 2011	$	245	$	—	$	(245	)	$	—	$	—	—



Purchases of TBAs and Forward Settling Agency Securities Designated as Hedging Instruments	Amount of Gain or (Loss) Recognized in OCI for Cash Flow Hedges (Effective Portion)		Amount of (Gain) or Loss Recognized in OCI for Cash Flow Hedges and Reclassified to OCI for Available-for-Sale Securities (Effective Portion)			Location of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)	Amount of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Nine months ended September 30, 2011	$	—	$	(3	)	Gain (loss) on derivative instruments and other securities, net	$	—

Derivatives Not Designated as Hedging Instruments

The table below summarizes fair value information about our derivatives outstanding that were not designated as hedging instruments as of September 30, 2012 and December 31, 2011 (in millions).



Derivatives Not Designated as Hedging Instruments	Balance Sheet Location	September 30, 2012			December 31, 2011
Interest rate swaps	Derivative assets, at fair value	$	6		$	13
Payer swaptions	Derivative assets, at fair value	57			11
Purchase of TBA and forward settling agency securities	Derivative assets, at fair value	186			54
Sale of TBA and forward settling agency securities	Derivative assets, at fair value	43			3
Markit IOS total return swaps - long	Derivative assets, at fair value	—			1
		$	292		$	82
Interest rate swaps	Derivative liabilities, at fair value	$	(1,442	)	$	(795	)
U.S. Treasury futures - short	Derivative liabilities, at fair value	—			(14		)
Purchase of TBA and forward settling agency securities	Derivative liabilities, at fair value	(20		)	—
Sale of TBA and forward settling agency securities	Derivative liabilities, at fair value	(100		)	(44		)
		$	(1,562	)	$	(853	)

Additionally, as of September 30, 2012 and December 31, 2011, we had obligations to return U.S. Treasury securities borrowed under reverse repurchase agreements accounted for as securities borrowing transactions at a fair value of $7.3 billion and $899 million, respectively. The borrowed securities were used to cover short sales of U.S. Treasury securities from which we received total proceeds of $7.2 billion and $880 million, respectively. The change in fair value of the borrowed securities is recorded in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income.

The tables below summarize the effect of derivative instruments not designated as hedges under ASC 815 on our consolidated statements of comprehensive income for the three and nine months ended September 30, 2012 and 2011 (in millions):



	Three Months Ended September 30, 2012
Derivatives Not Designated as Hedging Instruments	Notional Amount as of June 30, 2012		Additions	Settlement, Termination, Expiration or Exercise		Notional Amount as of September 30, 2012		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	7,447	36,956	(26,234	)	$	18,169	$	222
Sale of TBA and forward settling agency securities	$	10,851	53,318	(49,774	)	$	14,395	(173		)
Interest rate swaps	$	48,550	3,450	(3,150	)	$	48,850	(438		)
Payer swaptions	$	8,800	2,000	(2,250	)	$	8,550	(25		)
Short sales of U.S. Treasury securities	$	1,250	11,550	(5,505	)	$	7,295	(15		)
U.S. Treasury futures - short	$	1,919	—	(1,919	)	$	—	(27		)
Markit IOS total return swaps - long	$	37	—	(37	)	$	—	—
Markit IOS total return swaps - short	$	181	—	(181	)	$	—	—
								$	(456	)

________________________________


1.	Excludes a gain of $20 million from interest-only and principal-only securities and a loss of $24 million from debt of consolidated VIEs re-measured at fair value through earnings recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income for the three months ended September 30, 2012.



	Three Months Ended September 30, 2011
Derivatives Not Designated as Hedging Instruments	Notional Amount as of June 30, 2011		Additions	Additions Due to Hedge De-Designations	Settlement, Termination, Expiration or Exercise		Notional Amount as of September 30, 2011		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	3,432	19,881	—	(17,877	)	$	5,436	$	73
Sale of TBA and forward settling agency securities	$	4,282	37,867	—	(35,895	)	$	6,254	(146		)
Interest rate swaps	$	150	2,900	23,900	—		$	26,950	(3		)
Payer swaptions	$	4,050	250	—	(1,050	)	$	3,250	(33		)
Short sales of U.S. Treasury securities	$	1,464	3,450	—	(4,449	)	$	465	(92		)
US Treasury futures - long	$	—	350	—	—		$	350	2
Markit IOS total return swaps - long	$	683	65	—	(683	)	$	65	(19		)
Markit IOS total return swaps - short	$	309	323	—	(309	)	$	323	20
									$	(198	)

______________________

Excludes a loss of $28 million from interest-only and principal-only securities re-measured at fair value through earnings, a loss of $1 million for hedge ineffectiveness on our outstanding interest rate swaps and a gain of $5 million from U.S. Treasury securities in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income for the three months ended September 30, 2011.



	Nine Months Ended September 30, 2012
Derivatives Not Designated as Hedging Instruments	Notional Amount as of December 31, 2011		Additions	Settlement, Expiration or Exercise		Notional Amount as of September 30, 2012		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	3,699	90,498	(76,028	)	$	18,169	$	343
Sale of TBA and forward settling agency securities	$	3,803	131,030	(120,438	)	$	14,395	(402		)
Interest rate swaps	$	30,250	23,300	(4,700	)	$	48,850	(1,067		)
Payer swaptions	$	3,200	12,150	(6,800	)	$	8,550	(96		)
Short sales of U.S. Treasury securities	$	880	30,480	(24,065	)	$	7,295	(115		)
U.S. Treasury futures - short	$	783	3,838	(4,621	)	$	—	(91		)
Markit IOS total return swaps - long	$	41	—	(41	)	$	—	—
Markit IOS total return swaps - short	$	206	—	(206	)	$	—	—
								$	(1,428	)

________________________________

Excludes a loss of $1 million from U.S. Treasury securities, a gain of $19 million from interest-only and principal-only securities and a loss of $32 million from debt of consolidated VIEs re-measured at fair value through earnings recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income for the nine months ended September 30, 2012



	Nine Months Ended September 30, 2011
Derivatives Not Designated as Hedging Instruments	Notional Amount as of December 31, 2010		Additions		Additions Due to Hedge De-Designations	Settlement, Expiration or Exercise		Notional Amount as of September 30, 2011		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	512	42,222		—	(37,298	)	$	5,436	$	119
Sale of TBA and forward settling agency securities	$	1,361	88,795		—	(83,902	)	$	6,254	(291		)
Interest rate swaps	$	50	2,900		23,900	100		$	26,950	(8		)
Payer swaptions	$	850	4,450		—	(2,050	)	$	3,250	(58		)
Receiver Swaptions	$	—	250		—	(250	)	$	—	(1		)
Short sales of U.S. Treasury securities	$	250	11,974		—	(11,759	)	$	465	(92		)
Put Options	$	—	(200	)	—	200		$	—	1
U.S. Treasury futures - long	$	—	400		—	(50	)	$	350	2
Markit IOS total return swaps - long	$	—	1,154		—	(1,089	)	$	65	(6		)
Markit IOS total return swaps - short	$	—	636		—	(313	)	$	323	17
										$	(317	)

______________________

Excludes a loss of $24 million from interest-only securities re-measured at fair value through earnings, a loss of $2 million for hedge ineffectiveness on our outstanding interest rate swaps and a gain of $33 million from U.S. Treasury securities recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income for the nine months ended September 30, 2011.

The following tables summarize our interest rate swap agreements outstanding as of September 30, 2012 and December 31, 2011 (dollars in millions).



	September 30, 2012
Payer Interest Rate Swaps Not Designated as Hedging Instruments⁽¹⁾	Notional Amount		Average Fixed Pay Rate		Average Receive Rate		Net Estimated Fair Value			Average Maturity (Years)
Three years or less	$	17,150	1.15	%	0.30	%	$	(308	)	2.0
Greater than 3 years and less than/equal to 5 years	19,400		1.55	%	0.35	%	(767		)	4.2
Greater than 5 years and less than/equal to 7 years	7,100		1.41	%	0.43	%	(203		)	6.1
Greater than 7 years and less than/equal to 10 years	5,200		1.89	%	0.45	%	(158		)	9.4
Total Payer Interest Rate Swaps	$	48,850	1.43	%	0.35	%	$	(1,436	)	4.3

________________________


1.	Amounts include forward starting swaps of $3.1 billion ranging up to six months from September 30, 2012.



	December 31, 2011
Payer Interest Rate Swaps Not Designated as Hedging Instruments⁽¹⁾	Notional Amount		Average Fixed Pay Rate		Average Receive Rate		Net Estimated Fair Value			Average Maturity (Years)
Three years or less	$	11,350	1.22	%	0.30	%	$	(148	)	2.1
Greater than 3 years and less than/equal to 5 years	16,700		1.77	%	0.35	%	(607		)	3.9
Greater than 5 years and less than/equal to 7 years	950		1.56	%	0.57	%	(9		)	5.7
Greater than 7 years and less than/equal to 10 years	1,250		1.99	%	0.55	%	(18		)	8.2
Total Payer Interest Rate Swaps	$	30,250	1.57	%	0.35	%	$	(782	)	3.5

________________________


1.	Amounts include forward starting swaps of $2.6 billion ranging up to five months from December 31, 2011.

The following table summarizes our interest rate swaption agreements outstanding as of September 30, 2012 and December 31, 2011 (dollars in millions).



	Option					Underlying Swap
Payer Swaptions	Cost		Fair Value		Average Months to Expiration	Notional Amount		Average Fixed Pay Rate		Average Receive Rate	Average Term (Years)
As of September 30, 2012	$	152	$	57	19	$	8,550	3.30	%	1M / 3M LIBOR	7.7
As of December 31, 2011	$	49	$	11	7	$	3,200	3.41	%	1M / 3M LIBOR	7.7

The following table summarizes our contracts to purchase and sell TBA and specified agency securities on a forward basis as of September 30, 2012 and December 31, 2011 (in millions):



	September 30, 2012						December 31, 2011
Purchase and Sale Contracts for TBAs and Forward Settling Securities Not Designated as Hedging Instruments	Notional Amount			Fair Value			Notional Amount			Fair Value
TBA securities:
Purchase contracts	$	17,844		$	161		$	3,188		$	49
Sale contracts	(13,210		)	(54		)	(3,803		)	(41		)
TBA securities, net ⁽¹⁾	4,634			107			(615		)	8
Forward settling securities:
Purchase contracts	325			5			512			5
Sale contracts	(1,185		)	(3		)	—			—
Forward settling securities, net ⁽²⁾	(860		)	2			512			5
Total TBA and forward settling securities, net	$	3,774		$	109		$	(103	)	$	13

________________________


1.	Includes 15-year and 30-year TBA securities of varying coupons


2.	Includes 20-year and 30-year fixed securities of varying coupons

Credit Risk-Related Contingent Features

The use of derivatives creates exposure to credit risk relating to potential losses that could be recognized in the event that the counterparties to these instruments fail to perform their obligations under the contracts. We minimize this risk by limiting our counterparties to major financial institutions with acceptable credit ratings and monitoring positions with individual counterparties. In addition, we may be required to pledge assets as collateral for our derivatives, whose amounts vary over time based on the market value, notional amount and remaining term of the derivative contract. In the event of a default by a counterparty we may not receive payments provided for under the terms of our derivative agreements, and may have difficulty obtaining our assets pledged as collateral for our derivatives. The cash and cash equivalents and agency securities pledged as collateral for our derivative instruments is included in restricted cash and agency securities, respectively, on our consolidated balance sheets.

Each of our International Swaps and Derivatives Association ("ISDA") Master Agreements contains provisions under which we are required to fully collateralize our obligations under the swap instrument if at any point the fair value of the swap represents a liability greater than the minimum transfer amount contained within our agreements. We were also required to post initial collateral upon execution of certain of our swap transactions. If we breach any of these provisions, we will be required to settle our obligations under the agreements at their termination values.

Further, each of our ISDA Master Agreements also contains a cross default provision under which a default under certain of our other indebtedness in excess of a certain threshold causes an event of default under the agreement. Threshold amounts vary by lender. Following an event of default, we could be required to settle our obligations under the agreements at their termination values. Additionally, under certain of our ISDA Master Agreements, we could be required to settle our obligations under the agreements at their termination values if we fail to maintain certain minimum shareholders’ equity thresholds or our REIT status or if we fail to comply with limits on our leverage above certain specified levels.

As of September 30, 2012, the fair value and termination value of our interest rate swaps in a liability position related to these agreements was $1.4 billion. We had agency securities with fair values of $1.3 billion and restricted cash of $332 million pledged as collateral against our interest rate swaps, including initial collateral posted upon execution of interest rate swap and total return swap transactions.

- Definition

The entire disclosure for the entity's entire derivative instruments and hedging activities. Describes an entity's risk management strategies, derivatives in hedging activities and non-hedging derivative instruments, the assets, obligations, liabilities, revenues and expenses arising therefrom, and the amounts of and methodologies and assumptions used in determining the amounts of such items.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6441202&loc=d3e80720-113993

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 2
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+ Details

Fair Value Measurements

9 Months Ended

Sep. 30, 2012

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Disclosures [Text Block]

Fair Value Measurements

We determine the fair value of our agency securities and debt of consolidated VIEs based upon fair value estimates obtained from multiple third party pricing services and dealers. In determining fair value, third party pricing sources use various valuation approaches, including market and income approaches. Factors used by third party sources in estimating the fair value of an instrument may include observable inputs such as coupons, primary and secondary mortgage rates, pricing information, credit data, volatility statistics, and other market data that are current as of the measurement date. The availability of observable inputs can vary by instrument and is affected by a wide variety of factors, including the type of instrument, whether the instrument is new and not yet established in the marketplace and other characteristics particular to the instrument. Third party pricing sources may also use certain unobservable inputs, such as assumptions of future levels of prepayment, defaults and foreclosures, especially when estimating fair values for securities with lower levels of recent trading activity. We make inquiries of third party pricing sources to understand the significant inputs and assumptions they used to determine their prices. For further information regarding valuation of our derivative instruments, please refer to the discussion of derivative and other hedging instruments in Note 3.

We review the various third party fair value estimates and perform procedures to validate their reasonableness, including an analysis of the range of third party estimates for each position, comparison to recent trade activity for similar securities, and management review for consistency with market conditions observed as of the measurement date. While we do not adjust prices we obtain from third party pricing sources, we will exclude third party prices for securities from our determination of fair value if we determine (based on our validation procedures and our market knowledge and expertise) that the price is significantly different than observable market data would indicate and we cannot obtain an understanding from the third party source as to the significant inputs used to determine the price.

The validation procedures described above also influence our determination of the appropriate fair value measurement classification. We utilize a three-level valuation hierarchy for disclosure of fair value measurement. The valuation hierarchy is based upon the transparency of inputs to the valuation of an asset or liability as of the measurement date. A financial instrument's categorization within the hierarchy is based upon the lowest level of input that is significant to the fair value measurement. There were no transfers between hierarchy levels during the nine months ended September 30, 2012. The three levels of hierarchy are defined as follows:


•	Level 1 Inputs —Quoted prices (unadjusted) for identical unrestricted assets and liabilities in active markets that are accessible at the measurement date.


•	Level 2 Inputs —Quoted prices for similar assets and liabilities in active markets; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations whose inputs are observable or whose significant value drivers are observable.


•	Level 3 Inputs —Instruments with primarily unobservable market data that cannot be corroborated.

The following table provides a summary of our assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2012 and December 31, 2011 (dollars in millions):



	Fair Value Hierarchy
	Level 1		Level 2		Level 3
September 30, 2012
Assets:
Agency securities	$	—	$	89,640	$	—
Interest rate swaps	—		6		—
Other derivative instruments	—		286		—
Total	$	—	$	89,932	$	—
Liabilities:
Debt of consolidated VIEs	$	—	$	968	$	—
Obligation to return U.S. Treasury securities borrowed under reverse repurchase agreements	7,265		—		—
Interest rate swaps	—		1,442		—
Other derivative instruments	—		120		—
Total	$	7,265	$	2,530	$	—

December 31, 2011
Assets:
Agency securities	$	—	$	54,683	$	—
U.S. Treasury securities	101		—		—
Interest rate swaps	—		13		—
Other derivative instruments	—		69		—
Total	$	101	$	54,765	$	—
Liabilities:
Obligation to return U.S. Treasury securities borrowed under reverse repurchase agreements	$	899	$	—	$	—
U.S. Treasury futures	14		—		—
Interest rate swaps	—		795		—
Other derivative instruments	—		44		—
Total	$	913	$	839	$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

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+ Details

Stockholders' Equity	9 Months Ended
Stockholders' Equity	Sep. 30, 2012
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Stockholders' Equity Preferred Stock Offering Pursuant to our amended and restated certificate of incorporation, we are authorized to designate and issue up to 10.0 million shares of preferred stock in one or more classes or series. Our board of directors has designated 6.9 million shares as 8.000% Series A Cumulative Redeemable Preferred Stock ("Series A Preferred Stock"). As of September 30, 2012, we have 3.1 million of authorized but unissued shares of preferred stock. Our board of directors may designate additional series of authorized preferred stock ranking junior to or in parity with the Series A Preferred Stock or designate additional shares of the Series A Preferred Stock and authorize the issuance of such shares. In April 2012, we completed a public offering in which 6.9 million shares of our Series A Preferred Stock were sold to the underwriters at a price of $24.21 per share. Upon completion of the offering we received proceeds, net of offering expenses, of approximately $167 million. Our Series A Preferred Stock has no stated maturity and is not subject to any sinking fund or mandatory redemption. Under certain circumstances upon a change of control, the Series A Preferred Stock is convertible to shares of our common stock. Holders of Series A Preferred Stock have no voting rights, except under limited conditions, and holders are entitled to receive cumulative cash dividends at a rate of 8.00% per annum of the $25.00 per share liquidation preference before holders of our common stock are entitled to receive any dividends. Shares of our Series A Preferred Stock are redeemable at $25.00 per share plus accumulated and unpaid dividends (whether or not declared) exclusively at our option commencing on April 5, 2017, or earlier under certain circumstances intended to preserve our qualification as a REIT for Federal income tax purposes. Dividends are payable quarterly in arrears on the 15th day of each January, April, July and October. As of September 30, 2012, we had declared all required quarterly dividends on our Series A Preferred Stock. Common Stock Offering In March 2012, we completed a public offering in which 71.2 million shares of our common stock were sold to the underwriters at a price of $29.00 per share. Upon completion of the March offering, we received proceeds, net of offering expenses, of approximately $2.1 billion. In July 2012, we completed a public offering in which 36.8 million shares of our common stock were sold to the underwriters at a price of $33.70 per share. Upon completion of the July offering, we received proceeds, net of offering expenses, of approximately $1.2 billion. In both instances, the underwriters in the offering sold the shares of our common stock in one or more transactions on the NASDAQ Global Select Market, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale. At-the-Market Offering Program We have sales agreements with sales agents to publicly offer and sell shares of our common stock in privately negotiated and/or at-the-market transactions from time to time. During the nine months ended September 30, 2012, we sold 9.5 million shares of our common stock under such a sales agreement at an average price of $31.41 per share for proceeds, net of program costs, of $298 million. For the three months ended September 30, 2012, we did not sell any shares under the sales agreements. As of September 30, 2012, 16.7 million shares remain under the sales agreements. Dividend Reinvestment and Direct Stock Purchase Plan We sponsor a dividend reinvestment and direct stock purchase plan through which stockholders may purchase additional shares of our common stock by reinvesting some or all of the cash dividends received on shares of our common stock. Stockholders may also make optional cash purchases of shares of our common stock subject to certain limitations detailed in the plan prospectus. During the three and nine months ended September 30, 2012, there were no shares issued under the plan. As of September 30, 2012, 4.7 million shares remain under the plan.

- Definition

The entire disclosure for shareholders' equity, comprised of portions attributable to the parent entity and noncontrolling interest, if any, including other comprehensive income (as applicable). Including, but not limited to: (1) balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings; (2) accumulated balance for each classification of other comprehensive income and total amount of comprehensive income; (3) amount and nature of changes in separate accounts, including the number of shares authorized and outstanding, number of shares issued upon exercise and conversion, and for other comprehensive income, the adjustments for reclassifications to net income; (4) rights and privileges of each class of stock authorized; (5) basis of treasury stock, if other than cost, and amounts paid and accounting treatment for treasury stock purchased significantly in excess of market; (6) dividends paid or payable per share and in the aggregate for each class of stock for each period presented; (7) dividend restrictions and accumulated preferred dividends in arrears (in aggregate and per share amount); (8) retained earnings appropriations or restrictions, such as dividend restrictions; (9) impact of change in accounting principle, initial adoption of new accounting principle and correction of an error in previously issued financial statements; (10) shares held in trust for Employee Stock Ownership Plan (ESOP); (11) deferred compensation related to issuance of capital stock; (12) note received for issuance of stock; (13) unamortized discount on shares; (14) description, terms, and number of warrants or rights outstanding; (15) shares under subscription and subscription receivables, effective date of new retained earnings after quasi-reorganization and deficit eliminated by quasi-reorganization and, for a period of at least ten years after the effective date, the point in time from which the new retained dates; and (16) retroactive effective of subsequent change in capital structure.

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+ Details

Subsequent Event	9 Months Ended
Subsequent Event	Sep. 30, 2012
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event In October 2012, our Board of Directors adopted a plan that may provide for stock repurchases of up to $500 million of our outstanding shares of common stock through December 31, 2013. Shares of our common stock may be purchased in the open market, including through block purchases, or through privately negotiated transactions, or pursuant to any trading plan that may be adopted in accordance with Rule 10b5-1 of the Securities and Exchange Commission. The timing, manner, price and amount of any repurchases will be determined at our discretion and the program may be suspended, terminated or modified at any time for any reason. We intend to repurchase shares only when the purchase price is less than our estimate of our current net asset value per share of our common stock. Generally, when we repurchase our common stock at a discount to our net asset value, the net asset value of our remaining shares of common stock outstanding increases. In addition, we do not intend to repurchase any shares from directors, officers or other affiliates. The program does not obligate us to acquire any specific number of shares, and all repurchases will be made in accordance with SEC Rule 10b-18, which sets certain restrictions on the method, timing, price and volume of stock repurchases.

Summary of Significant Accounting Policies (Policy)	9 Months Ended
Summary of Significant Accounting Policies (Policy)	Sep. 30, 2012
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Consolidation, Variable Interest Entity, Policy [Policy Text Block]	Variable Interest Entities ASC Topic 810, Consolidation (“ASC 810”), requires an enterprise to consolidate a variable interest entity ("VIE") if it is deemed the primary beneficiary of the VIE. Further, ASC 810 requires a qualitative assessment to determine the primary beneficiary of a VIE and ongoing assessments of whether an enterprise is the primary beneficiary of a VIE as well as additional disclosures for entities that have variable interests in VIEs. We have entered into transactions involving CMO trusts (e.g. a VIE) whereby, in each case, we transferred agency MBS to an investment bank in exchange for cash proceeds and at the same time entered into a commitment with the same investment bank to purchase to-be-issued securities collateralized by the agency MBS transferred, which resulted in our consolidation of the CMO trusts. We will consolidate a CMO trust if we are the CMO trust’s primary beneficiary; that is, if we have a variable interest that provides us with a controlling financial interest in the CMO trust. An entity is deemed to have a controlling financial interest if the entity has the power to direct the activities of a VIE that most significantly impact the VIE’s economic performance and the obligation to absorb losses of or right to receive benefits from the VIE that could potentially be significant to the VIE. As part of the qualitative assessment in determining if we have a controlling financial interest, we evaluate whether we control the selection of financial assets transferred to the CMO trust. Agency MBS transferred to consolidated VIEs are reported on our consolidated balance sheets in agency securities transferred to consolidated variable interest entities, at fair value and can only be used to settle the obligations of each respective VIE. We report debt issued in connection with the CMO trusts on our consolidated balance sheets in debt of consolidated VIEs, at fair value, which represents tranches within the trusts sold to third-parties and excludes tranches acquired by us that eliminate in consolidation. The third-party beneficial interest holders in the VIEs have no recourse against our general credit. For transactions entered into subsequent to December 31, 2011, we have elected the option to account for the consolidated debt at fair value, with changes in fair value reflected in earnings during the period in which they occur. We believe this election more appropriately reflects our financial position as both the consolidated assets and consolidated debt are presented in a consistent manner on our consolidated balance sheets. We estimate the fair value of the consolidated debt based on a market approach using Level 2 inputs from third-party pricing services and dealer quotes
Investment Securities	Investment Securities ASC Topic 320, Investments—Debt and Equity Securities (“ASC 320”), requires that at the time of purchase, we designate a security as held-to-maturity, available-for-sale or trading, depending on our ability and intent to hold such security to maturity. Securities classified as trading and available-for-sale are reported at fair value, while securities classified as held-to-maturity are reported at amortized cost. We may, from time to time, sell any of our investment securities as part of our overall management of our investment portfolio. Accordingly, we typically designate our investment securities as available-for-sale. All securities classified as available-for-sale are reported at fair value, with unrealized gains and losses reported in other comprehensive income ("OCI") a separate component of stockholders’ equity. Upon the sale of a security, we determine the cost of the security and the amount of unrealized gains or losses to reclassify out of accumulated OCI into earnings based on the specific identification method. Interest-only securities and inverse interest-only securities (collectively referred to as “interest-only securities”) represent our right to receive a specified proportion of the contractual interest flows of specific agency CMO securities. Principal-only securities represent our right to receive the contractual principal flows of specific agency CMO securities. Interest-only and principal-only securities are measured at fair value through earnings in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income. Our investments in interest-only and principal-only securities are included in agency MBS securities, at fair value on the accompanying consolidated balance sheets. We estimate the fair value of our investment securities based on a market approach using Level 2 inputs from third-party pricing services and dealer quotes. The third-party pricing services use pricing models that incorporate such factors as coupons, primary and secondary mortgage rates, prepayment speeds, spread to the Treasury and interest rate swap curves, convexity, duration, periodic and life caps and credit enhancements. The dealer quotes incorporate common market pricing methods, including a spread measurement to the Treasury or interest rate swap curve as well as underlying characteristics of the particular security including coupon, periodic and life caps, rate reset period, issuer, additional credit support and expected life of the security. Refer to Note 7 for further discussion of fair value measurements. We evaluate securities for other-than-temporary impairment (“OTTI”) on at least a quarterly basis, and more frequently when economic or market conditions warrant such evaluation. The determination of whether a security is other-than-temporarily impaired involves judgments and assumptions based on subjective and objective factors. When an investment security is impaired, an OTTI is considered to have occurred if (i) we intend to sell the investment security (i.e. a decision has been made as the reporting date) or (ii) it is more likely than not that we will be required to sell the investment security before recovery of its amortized cost basis. If we intend to sell the security or if it is more likely than not that we will be required to sell the investment security before recovery of its amortized cost basis, the entire amount of the impairment loss, if any, is recognized in earnings as a realized loss and the cost basis of the security is adjusted to its fair value. We did not recognize any OTTI charges on any of our investment securities for the three and nine months ended September 30, 2012 and 2011.
Interest Income	Interest Income Interest income is accrued based on the outstanding principal amount of the investment securities and their contractual terms. Premiums and discounts associated with the purchase of investment securities are amortized or accreted into interest income over the projected lives of the securities, including contractual payments and estimated prepayments using the interest method in accordance with ASC Subtopic 310-20, Receivables—Nonrefundable Fees and Other Costs (“ASC 310-20”). We estimate long-term prepayment speeds of our agency securities using a third-party service and market data. The third-party service estimates prepayment speeds using models that incorporate the forward yield curve, current mortgage rates, current mortgage rates of the outstanding loans, loan age, volatility and other factors. We review the prepayment speeds estimated by the third-party service and compare the results to market consensus prepayment speeds, if available. We also consider historical prepayment speeds and current market conditions to validate the reasonableness of the prepayment speeds estimated by the third-party service and, based on our Manager’s judgment, we may make adjustments to their estimates. Actual and anticipated prepayment experience is reviewed quarterly and effective yields are recalculated when differences arise between (i) our previously estimated future prepayments and (ii) actual prepayments to date plus current estimated future prepayments. If the actual and estimated future prepayment experience differs from our prior estimate of prepayments, we are required to record an adjustment in the current period to the amortization or accretion of premiums and discounts for the cumulative difference in the effective yield through the reporting date. The yield on our adjustable rate securities further assumes that the securities reset at a rate equal to the underlying index rate in effect as of the date we acquired the security plus the stated margin.
Derivative and other Hedging Instruments	Interest rate swap agreements We use interest rate swaps to economically hedge the variable cash flows associated with borrowings made under our repurchase agreement facilities. Under our interest rate swap agreements, we typically pay a fixed rate and receive a floating rate based on one or three-month LIBOR ("payer swap") with terms up to 10 years, which has the effect of modifying the repricing characteristics of our repurchase agreements and cash flows on such liabilities. We estimate the fair value of interest rate swaps using a third-party pricing model. The third-party pricing model incorporates such factors as the LIBOR curve and the pay rate on the interest rate swaps. We also incorporate both our own and our counterparties’ nonperformance risk in estimating the fair value of our interest rate swaps. In considering the effect of nonperformance risk, we consider the impact of netting and credit enhancements, such as collateral postings and guarantees, and have concluded that our own and our counterparty risk is not significant to the overall valuation of these agreements. Interest rate swaptions We purchase interest rate swaptions to help mitigate the potential impact of increases or decreases in interest rates on the performance of our investment portfolio (referred to as “convexity risk”). The interest rate swaptions provide us the option to enter into an interest rate swap agreement for a predetermined notional amount, stated term and pay and receive interest rates in the future. Our swaption agreements typically provide us the option to enter into a pay fixed rate interest rate swap, which we refer as “payer swaptions”. We may also enter into swaption agreements that provide us the option to enter into a receive fixed interest rate swap, which we refer to as "receiver swaptions". The premium paid for interest rate swaptions is reported as an asset in our consolidated balance sheets. The premium is valued at an amount equal to the fair value of the swaption that would have the effect of closing the position adjusted for nonperformance risk, if any. The difference between the premium and the fair value of the swaption is reported in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income. If a swaption expires unexercised, the loss on the swaption would be equal to the premium paid. If we sell or exercise a swaption, the realized gain or loss on the swaption would be equal to the difference between the cash or the fair value of the underlying interest rate swap received and the premium paid. We estimate the fair value of interest rate swaptions using a third-party pricing model based on the fair value of the future interest rate swap that we have the option to enter into as well as the remaining length of time that we have to exercise the option, adjusted for non-performance risk, if any. TBA securities A TBA security is a forward contract for the purchase ("long position") or sale ("short position") of agency MBS at a predetermined price, face amount, issuer, coupon and stated maturity on an agreed-upon future date. The specific agency MBS delivered into the contract upon the settlement date, published each month by the Securities Industry and Financial Markets Association, are not known at the time of the transaction. The difference between the contract price and the fair value of the TBA security is reported in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income. Upon settlement of the TBA contract, the realized gain or loss on the TBA contract is equal to the difference between the fair value of the underlying agency MBS physically received/delivered and the contract price, or if cash settled, is equal to the net cash amount paid or received. We estimate the fair value of TBA securities based on similar methods used to value our agency MBS securities. Forward commitments to purchase or sell specified agency MBS We enter into forward commitments to purchase or sell specified agency MBS from time to time as a means of acquiring assets or as a hedge against short-term changes in interest rates. We account for contracts for the purchase or sale of specified agency MBS securities as derivatives if the delivery of the specified agency MBS and settlement extends beyond the shortest period possible for that type of security. Realized and unrealized gains and losses associated with forward commitments accounted for as derivatives are recognized in our consolidated statements of comprehensive income in gain (loss) on derivative instruments and other securities, net. We estimate the fair value of forward commitments to purchase or sell specified agency MBS based on similar methods used to value agency MBS, as well as the remaining length of time of the forward commitment. U.S. Treasury securities We purchase or sell short U.S. Treasury securities and U.S. Treasury futures contracts to help mitigate the potential impact of changes in interest rates on the performance of our portfolio. We borrow securities to cover short sales of U.S. Treasury securities under reverse repurchase agreements. We account for these as securities borrowing transactions and recognize an obligation to return the borrowed securities at fair value on the balance sheet based on the value of the underlying borrowed securities as of the reporting date. Gains and losses associated with purchases and short sales of U.S. Treasury securities are recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income. Total return swaps We enter into total return swaps to obtain exposure to a security or market sector without owning such security or investing directly in that market sector. Total return swaps are agreements in which there is an exchange of cash flows whereby one party commits to make payments based on the total return (coupon plus the mark-to-market movement) of an underlying instrument or index in exchange for fixed or floating rate interest payments. To the extent the total return of the instrument or index underlying the transaction exceeds or falls short of the offsetting interest rate obligation, we will receive a payment from or make a payment to the counterparty. The primary total return swap index in which we invest is the Markit IOS Index. Total return swaps based on the Markit IOS Index are intended to synthetically replicate the performance of interest-only securities. We determine the fair value of our total return swaps based on published index prices. Gains and losses associated with changes in market value of the underlying index and coupon interest are recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statements of comprehensive income. Derivative and other Hedging Instruments We use a variety of derivative instruments to economically hedge a portion of our exposure to market risks, including interest rate and prepayment risk. The objective of our risk management strategy is to reduce fluctuations in net book value over a range of interest rate scenarios. In particular, we attempt to mitigate the risk of the cost of our variable rate liabilities increasing during a period of rising interest rates. The principal instruments that we use are interest rate swaps and options to enter into interest rate swaps (“interest rate swaptions”). We also purchase or sell to-be-announced agency MBS forward contracts (“TBAs”), specified agency MBS on a forward basis, U.S. Treasury securities and U.S. Treasury futures contracts. We may also purchase or write put or call options on TBA securities and invest in other types of mortgage derivatives, such as interest-only securities, and synthetic total return swaps, such as the Markit IOS Synthetic Total Return Swap Index (“Markit IOS Index”). We account for derivative instruments in accordance with ASC Topic 815, Derivatives and Hedging (“ASC 815”). ASC 815 requires an entity to recognize all derivatives as either assets or liabilities in the balance sheet and to measure those instruments at fair value. Hedging instruments that are not derivatives under ASC 815 are accounted for as securities in accordance with ASC 320. The accounting for changes in the fair value of derivative instruments depends on whether the instruments are designated and qualify as part of a hedging relationship pursuant to ASC 815. Changes in fair value related to derivatives not in hedge designated relationships are recorded in gain (loss) on derivative instruments and other securities, net; whereas changes in fair value related to derivatives in hedge designated relationships are initially recorded in OCI and later reclassified to income at the time that the hedged transactions affect earnings. Any portion of the changes in fair value due to hedge ineffectiveness is immediately recognized in gain (loss) on derivative instruments and other securities, net. Our derivative agreements and repurchase agreements generally contain provisions that allow for netting or setting off receivables and payables with each counterparty. We report amounts in our consolidated balance sheets on a gross basis without regard for such rights of offset or master netting arrangements. Derivatives in a gain position are reported as derivative assets at fair value and derivatives in a loss position are reported as derivative liabilities at fair value in our consolidated balance sheets. In our consolidated statements of cash flows, cash receipts and payments related to derivative instruments are classified according to the underlying nature or purpose of the derivative transaction, generally in the operating section for derivatives designated in hedging relationships and the investing section for derivatives not designated in hedging relationships. The use of derivatives creates exposure to credit risk relating to potential losses that could be recognized in the event that the counterparties to these instruments fail to perform their obligations under the contracts. We attempt to minimize this risk by limiting our counterparties to major financial institutions with acceptable credit ratings, monitoring positions with individual counterparties and adjusting posted collateral as required.
Reclassifications	Reclassifications Certain prior period amounts in the consolidated financial statements have been reclassified to conform to the current period presentation.
Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Derivative and other Hedging Instruments	Discontinuation of hedge accounting for interest rate swap agreements Prior to the third quarter of 2011, we entered into interest rate swap agreements typically with the intention of qualifying for hedge accounting under ASC 815. However, as of September 30, 2011, we elected to discontinue hedge accounting for our interest rate swaps. Our net asset value was not impacted by our election to discontinue hedge accounting since our net asset value is the same irrespective of whether we apply hedge accounting. Upon discontinuation of hedge accounting, the net deferred loss related to our de-designated interest rate swaps remained in accumulated OCI and is being reclassified from accumulated OCI into interest expense on a straight-line basis over the remaining term of each interest rate swap. Although the reclassification of accumulated OCI into interest expense is similar to as if the interest rate swaps had not been de-designated, the actual net periodic interest costs associated with our de-designated interest rates swaps may be more or less than amounts reclassified into interest expense. The difference, as well as net periodic interest costs on interest rate swaps that were never in a hedge designation, along with subsequent changes in the fair value of our interest rates swaps, is reported in our consolidated statement of comprehensive income in gain (loss) on derivative instruments and other securities, net.

- Definition

Disclosure of accounting policy for consolidation to describe the significant judgments and assumptions made in determining whether a variable interest held by the entity requires the variable interest entity to be consolidated and (or) disclose information about its involvement with the variable interest entity; the methodology used by the entity for determining whether or not it is the primary beneficiary of the variable interest entity; and the significant factors considered and judgments made in determining that the power to direct the activities that significantly impact the economic performance of the variable interest entity are shared (as defined).

+ References

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+ Details

- Definition

Disclosure of accounting policy for its derivative instruments and hedging activities.

+ References

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+ Details

- Definition

Disclosure of accounting policy for investments in financial assets, including marketable securities (debt and equity securities with readily determinable fair values), investments accounted for under the equity method and cost method, securities borrowed and loaned, and repurchase and resale agreements. For marketable securities, the disclosure may include the entity's accounting treatment for transfers between investment categories and how the fair values for such securities are determined. Also, for all investments, an entity may describe its policy for assessing, recognizing and measuring impairment of the investment.

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+ Details

Investment Securities (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2012

Dec. 31, 2011

Available-for-sale Securities [Abstract]

Agency Securities [Table Text Block]

The following tables summarize our investments in agency MBS as of September 30, 2012 (dollars in millions):



	September 30, 2012
Agency MBS	Fannie Mae			Freddie Mac			Ginnie Mae			Total
Available-for-sale agency MBS:
Agency MBS, par	$	64,352		$	17,512		$	260		$	82,124
Unamortized premium	3,319			827			12			4,158
Amortized cost	67,671			18,339			272			86,282
Gross unrealized gains	2,161			617			6			2,784
Gross unrealized losses	(1		)	—			—			(1		)
Total available-for-sale agency MBS, at fair value	69,831			18,956			278			89,065
Agency MBS remeasured at fair value through earnings:
Interest-only and principal-only strips, amortized cost ⁽¹⁾	508			60			—			568
Gross unrealized gains	30			1			—			31
Gross unrealized losses	(12		)	(12		)	—			(24		)
Total agency MBS remeasured at fair value through earnings	526			49			—			575
Total agency MBS, at fair value	$	70,357		$	19,005		$	278		$	89,640
Weighted average coupon as of September 30, 2012⁽²⁾	3.74		%	3.88		%	3.78		%	3.77		%
Weighted average yield as of September 30, 2012⁽³⁾	2.56		%	2.82		%	1.60		%	2.61		%
Weighted average yield for the three months ended September 30, 2012⁽³⁾	2.53		%	2.62		%	1.54		%	2.55		%
Weighted average yield for the nine months ended September 30, 2012⁽³⁾	2.82		%	2.85		%	1.64		%	2.82		%

________________________


2.	The weighted average coupon includes the interest cash flows from our interest-only agency MBS strips taken together with the interest cash flows from our fixed-rate, adjustable-rate and CMO agency MBS as a percentage of the par value of our agency MBS (excluding the UPB of our interest-only securities) as of September 30, 2012.


3.	Incorporates a weighted average future constant prepayment rate assumption of 14% based on forward rates as of September 30, 2012 and a weighted average reset rate for adjustable rate securities of 2.67%, which is equal to a weighted average underlying index rate of 0.96% based on the current spot rate in effect as of the date we acquired the securities and a weighted average margin of 1.71%

The following tables summarize our investments in agency MBS as of December 31, 2011 (dollars in millions):



	December 31, 2011
Agency MBS	Fannie Mae			Freddie Mac			Ginnie Mae			Total
Available-for-sale agency MBS:
Agency MBS, par	$	37,232		$	13,736		$	258		$	51,226
Unamortized premium	1,659			606			12			2,277
Amortized cost	38,891			14,342			270			53,503
Gross unrealized gains	680			324			3			1,007
Gross unrealized losses	(4		)	(2		)	—			(6		)
Available-for-sale agency MBS, at fair value	39,567			14,664			273			54,504
Agency MBS remeasured at fair value through earnings:
Interest-only and principal-only strips, amortized cost ⁽¹⁾	124			67			—			191
Gross unrealized gains	6			3			—			9
Gross unrealized losses	(8		)	(13		)	—			(21		)
Agency MBS remeasured at fair value through earnings	122			57			—			179
Total agency MBS, at fair value	$	39,689		$	14,721		$	273		$	54,683
Weighted average coupon as of December 31, 2011 ⁽²⁾	4.18		%	4.39		%	3.74		%	4.23		%
Weighted average yield as of December 31, 2011 ⁽³⁾	3.03		%	3.20		%	1.71		%	3.07		%
Weighted average yield for the year ended December 31, 2011 ⁽³⁾	3.19		%	3.20		%	2.05		%	3.19		%

________________________


1.	The UPB of our interest-only securities was $1.1 billion and the weighted average contractual interest we are entitled to receive was 5.52% of this amount as of December 31, 2011. The par value of our principal-only agency MBS strips was $40 million as of December 31, 2011.


2.	The weighted average coupon includes the interest cash flows from our interest-only securities taken together with the interest cash flows from our fixed-rate, adjustable-rate and CMO securities as a percentage of the par value of our agency securities (excluding the UPB of our interest-only securities) as of December 31, 2011.


3.	Incorporates a weighted average future constant prepayment rate assumption of 14% based on forward rates as of December 31, 2011 and a weighted average reset rate for adjustable rate securities of 2.71%, which is equal to a weighted average underlying index rate of 0.94% based on the current spot rate in effect as of the date we acquired the securities and a weighted average margin of 1.77%.



	December 31, 2011
Agency MBS	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Fixed-Rate	$	50,535	$	952	$	(4	)	$	51,483
Adjustable-Rate	2,725		51		(2		)	2,774
CMO	243		4		—			247
Interest-only strips	191		9		(21		)	179
Total agency MBS	$	53,694	$	1,016	$	(27	)	$	54,683

Summary Of Agency Securities Estimated Weighted Average Life Classifications



	September 30, 2012						December 31, 2011
Estimated Weighted Average Life of Agency MBS Classified as Available-for-Sale	Fair Value		Amortized Cost		Weighted Average Coupon		Fair Value		Amortized Cost		Weighted Average Coupon
Less than or equal to 1 year	$	—	$	—	—	%	$	214	$	210	4.61	%
Greater than 1 year and less than/equal to 3 years	9,902		9,656		3.17	%	3,392		3,338		4.38	%
Greater than 3 years and less than/equal to 5 years	39,737		38,442		3.66	%	26,168		25,616		3.99	%
Greater than 5 years and less than/equal to 10 years	38,832		37,600		3.80	%	24,710		24,320		4.19	%
Greater than 10 years	594		584		3.55	%	20		19		5.02	%
Total	$	89,065	$	86,282	3.66	%	$	54,504	$	53,503	4.11	%

Summary Of Agency Securities Pledged As Collateral Under Repurchase Agreements by Remaining Maturity



	September 30, 2012						December 31, 2011
Securities Pledged by Remaining Maturity of Repurchase Agreements and Debt of Consolidated VIEs	Fair Value of Pledged Securities		Amortized Cost of Pledged Securities		Accrued Interest on Pledged Securities		Fair Value of Pledged Securities		Amortized Cost of Pledged Securities		Accrued Interest on Pledged Securities
Agency MBS:
Less than 30 days	$	30,861	$	29,867	$	86	$	19,772	$	19,361	$	63
31 - 59 days	17,739		17,134		51		16,964		16,648		55
60 - 90 days	17,822		17,242		50		8,337		8,179		26
Greater than 90 days	18,852		18,348		52		5,240		5,154		17
Total agency MBS	85,274		82,591		239		50,313		49,342		161
U.S. Treasury securities:
1 day	—		—		—		101		101		—
Total securities	$	85,274	$	82,591	$	239	$	50,414	$	49,443	$	161

Schedule of Investments Owned and Pledged as Collateral [Table Text Block]



	September 30, 2012
Assets Pledged	Repurchase Agreements		Debt of Consolidated VIEs		Derivative Agreements		Prime Broker Agreements		Total
Agency MBS - fair value	$	83,654	$	1,620	$	1,255	$	157	$	86,686
Accrued interest on pledged securities	234		5		4		—		243
Restricted cash	—		—		369		—		369
Total	$	83,888	$	1,625	$	1,628	$	157	$	87,298



	December 31, 2011
Assets Pledged	Repurchase Agreements		Debt of Consolidated VIEs		Derivative Agreements		Prime Broker Agreements		Total
Agency MBS - fair value	$	50,255	$	58	$	644	$	87	$	51,044
U.S. Treasury securities - fair value	101		—		—		—		101
Accrued interest on pledged securities	161		—		2		—		163
Restricted cash	—		—		336		—		336
Total	$	50,517	$	58	$	982	$	87	$	51,644

Summary of Changes in Accumulated OCI for Agency Securitie [Table Text Block]

The following table summarizes changes in accumulated OCI for our available-for-sale securities for the three and nine months ended September 30, 2012 and 2011 (in millions):



Agency Securities Classified as Available-for-Sale	Beginning OCI Balance			Unrealized Gains and (Losses), Net	Reversal of Prior Period Unrealized (Gains) and Losses, Net on Realization		Ending OCI Balance
Three months ended September 30, 2012	$	1,585		1,400	(210	)	$	2,775
Three months ended September 30, 2011	$	251		802	(266	)	$	787
Nine months ended September 30, 2012	$	1,002		2,616	(843	)	$	2,775
Nine months ended September 30, 2011	$	(28	)	1,178	(363	)	$	787

Components of Investment Securities [Table Text Block]



	September 30, 2012
Agency MBS	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Fixed-Rate	$	85,136	$	2,747	$	(1	)	$	87,882
Adjustable-Rate	960		32		—			992
CMO	186		5		—			191
Interest-only and principal-only strips	568		31		(24		)	575
Total agency MBS	$	86,850	$	2,815	$	(25	)	$	89,640



	December 31, 2011
Agency MBS	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Fixed-Rate	$	50,535	$	952	$	(4	)	$	51,483
Adjustable-Rate	2,725		51		(2		)	2,774
CMO	243		4		—			247
Interest-only strips	191		9		(21		)	179
Total agency MBS	$	53,694	$	1,016	$	(27	)	$	54,683

Summary of Continuous Unrealized Loss Position of Available for Sale Securities [Table Text Block]



	Unrealized Loss Position For
	Less than 12 Months					12 Months or More				Total
Agency Securities Classified as Available-for-Sale	Estimated Fair Value		Unrealized Loss			Estimated Fair Value		Unrealized Loss		Estimated Fair Value		Unrealized Loss
September 30, 2012	$	436	$	(1	)	$	—	$	—	$	436	$	(1	)
December 31, 2011	$	1,135	$	(6	)	$	—	$	—	$	1,135	$	(6	)

Summary of Net Gain from Sale of Agency Securities [Table Text Block]

The following table is a summary of our net gain from the sale of agency MBS for the three and nine months ended September 30, 2012 and 2011 (in millions):



	Three Months Ended						Nine Months Ended
Agency MBS	September 30, 2012			September 30, 2011			September 30, 2012			September 30, 2011
Agency MBS sold, at cost	$	(10,172	)	$	(14,046	)	$	(45,258	)	$	(26,429	)
Proceeds from agency MBS sold ⁽¹⁾	10,382			14,309			46,101			26,790
Net gains on sale of agency MBS	$	210		$	263		$	843		$	361

Gross gains on sale of agency MBS	$	210		$	268		$	855		$	377
Gross losses on sale of agency MBS	—			(5		)	(12		)	(16		)
Net gains on sale of agency MBS	$	210		$	263		$	843		$	361

________________________


1.	Proceeds include cash received during the period, plus receivable for agency MBS sold during the period as of period end.

Repurchase Agreements and Other Debt (Tables)

9 Months Ended

Sep. 30, 2012

Disclosure of Repurchase Agreements [Abstract]

Schedule of Borrowings under Repurchase Agreements and Weighted Average Interest Rates [Table Text Block]



	September 30, 2012					December 31, 2011
Original Maturity	Repurchase Agreements		Weighted Average Interest Rate		Weighted Average Days to Maturity	Repurchase Agreements		Weighted Average Interest Rate		Weighted Average Days to Maturity
Agency MBS:
1 month or less	$	4,724	0.43	%	12	$	2,558	0.43	%	10
1-3 months	31,253		0.43	%	37	24,518		0.39	%	32
4-6 months	25,571		0.45	%	72	16,475		0.37	%	53
7-9 months	8,641		0.49	%	92	2,423		0.45	%	141
10-12 months	7,547		0.57	%	266	1,006		0.53	%	244
13-24 months	693		0.67	%	613	600		0.51	%	268
25-36 months	825		0.72	%	992	—		—		—
Total agency MBS	79,254		0.46	%	89	47,580		0.40	%	51
U.S. Treasury securities:
1 day	—		—		—	101		0.40	%	1
Total / Weighted Average	$	79,254	0.46	%	89	$	47,681	0.40	%	51

Derivative and Other Hedging Instruments (Tables)

3 Months Ended

9 Months Ended

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Derivative [Line Items]

Schedule of Interest Rate Swaption Agreements Outstandin [Table Text Block]

The following table summarizes our interest rate swaption agreements outstanding as of September 30, 2012 and December 31, 2011 (dollars in millions).



	Option					Underlying Swap
Payer Swaptions	Cost		Fair Value		Average Months to Expiration	Notional Amount		Average Fixed Pay Rate		Average Receive Rate	Average Term (Years)
As of September 30, 2012	$	152	$	57	19	$	8,550	3.30	%	1M / 3M LIBOR	7.7
As of December 31, 2011	$	49	$	11	7	$	3,200	3.41	%	1M / 3M LIBOR	7.7

Summary of Outstanding Interest Rate Swaps Designated as Hedging Instruments



Interest Rate Swaps Designated as Hedging Instruments	Beginning Notional Amount		Additions	Expirations / Terminations		Hedge De-Designations		Ending Notional Amount
Three months ended September 30, 2011	$	22,000	2,100	(200	)	(23,900	)	$	—
Nine months ended September 30, 2011	$	6,450	17,900	(450	)	(23,900	)	$	—

Summary of Outstanding Forward Contracts Designated as Hedging Instruments

The following tables summarize information about these securities and their effect on our consolidated statement of comprehensive income for the nine months ended September 30, 2011 (dollars in millions). We did not designate any such agreements as cash flow hedges during the three months ended September 30, 2011 and the three and nine months ended September 30, 2012.



Purchases of TBAs and Forward Settling Agency Securities Designated as Hedging Instruments	Beginning Notional Amount		Additions		Settlement / Expirations			Ending Notional Amount		Fair Value as of Period End		Average Maturity as of Period End (Months)
Nine Months Ended September 30, 2011	$	245	$	—	$	(245	)	$	—	$	—	—

Effect of Interest Rate Swaps Designated as Hedges



Purchases of TBAs and Forward Settling Agency Securities Designated as Hedging Instruments	Amount of Gain or (Loss) Recognized in OCI for Cash Flow Hedges (Effective Portion)		Amount of (Gain) or Loss Recognized in OCI for Cash Flow Hedges and Reclassified to OCI for Available-for-Sale Securities (Effective Portion)			Location of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)	Amount of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Nine months ended September 30, 2011	$	—	$	(3	)	Gain (loss) on derivative instruments and other securities, net	$	—

Summary of Long and Short Position of Derivative Instruments

The following table summarizes our contracts to purchase and sell TBA and specified agency securities on a forward basis as of September 30, 2012 and December 31, 2011 (in millions):



	September 30, 2012						December 31, 2011
Purchase and Sale Contracts for TBAs and Forward Settling Securities Not Designated as Hedging Instruments	Notional Amount			Fair Value			Notional Amount			Fair Value
TBA securities:
Purchase contracts	$	17,844		$	161		$	3,188		$	49
Sale contracts	(13,210		)	(54		)	(3,803		)	(41		)
TBA securities, net ⁽¹⁾	4,634			107			(615		)	8
Forward settling securities:
Purchase contracts	325			5			512			5
Sale contracts	(1,185		)	(3		)	—			—
Forward settling securities, net ⁽²⁾	(860		)	2			512			5
Total TBA and forward settling securities, net	$	3,774		$	109		$	(103	)	$	13

________________________


1.	Includes 15-year and 30-year TBA securities of varying coupons


2.	Includes 20-year and 30-year fixed securities of varying coupons

Schedule Of Effect Interest Rate Swaps Designated As Hedges



Interest Rate Swaps Designated as Hedging Instruments:	Amount of Gain or (Loss) Recognized in OCI (Effective Portion)			Location of Gain or (Loss) Reclassified from OCI into Earnings (Effective Portion)	Amount of (Gain) or Loss Reclassified from OCI into Earnings (Effective Portion)		Location of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)	Amount of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)
Three Months Ended September 30, 2011	$	(512	)	Interest expense	(71	)	Gain (loss) on derivative instruments and other securities, net	$	(1	)
Nine Months Ended September 30, 2011	$	(707	)	Interest expense	(140	)	Gain (loss) on derivative instruments and other securities, net	$	(2	)

Schedule of Outstanding Derivatives Not Designated as Hedging Instruments [Table Text Block]

The table below summarizes fair value information about our derivatives outstanding that were not designated as hedging instruments as of September 30, 2012 and December 31, 2011 (in millions).



Derivatives Not Designated as Hedging Instruments	Balance Sheet Location	September 30, 2012			December 31, 2011
Interest rate swaps	Derivative assets, at fair value	$	6		$	13
Payer swaptions	Derivative assets, at fair value	57			11
Purchase of TBA and forward settling agency securities	Derivative assets, at fair value	186			54
Sale of TBA and forward settling agency securities	Derivative assets, at fair value	43			3
Markit IOS total return swaps - long	Derivative assets, at fair value	—			1
		$	292		$	82
Interest rate swaps	Derivative liabilities, at fair value	$	(1,442	)	$	(795	)
U.S. Treasury futures - short	Derivative liabilities, at fair value	—			(14		)
Purchase of TBA and forward settling agency securities	Derivative liabilities, at fair value	(20		)	—
Sale of TBA and forward settling agency securities	Derivative liabilities, at fair value	(100		)	(44		)
		$	(1,562	)	$	(853	)



	Nine Months Ended September 30, 2012
Derivatives Not Designated as Hedging Instruments	Notional Amount as of December 31, 2011		Additions	Settlement, Expiration or Exercise		Notional Amount as of September 30, 2012		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	3,699	90,498	(76,028	)	$	18,169	$	343
Sale of TBA and forward settling agency securities	$	3,803	131,030	(120,438	)	$	14,395	(402		)
Interest rate swaps	$	30,250	23,300	(4,700	)	$	48,850	(1,067		)
Payer swaptions	$	3,200	12,150	(6,800	)	$	8,550	(96		)
Short sales of U.S. Treasury securities	$	880	30,480	(24,065	)	$	7,295	(115		)
U.S. Treasury futures - short	$	783	3,838	(4,621	)	$	—	(91		)
Markit IOS total return swaps - long	$	41	—	(41	)	$	—	—
Markit IOS total return swaps - short	$	206	—	(206	)	$	—	—
								$	(1,428	)

________________________________



	Nine Months Ended September 30, 2011
Derivatives Not Designated as Hedging Instruments	Notional Amount as of December 31, 2010		Additions		Additions Due to Hedge De-Designations	Settlement, Expiration or Exercise		Notional Amount as of September 30, 2011		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	512	42,222		—	(37,298	)	$	5,436	$	119
Sale of TBA and forward settling agency securities	$	1,361	88,795		—	(83,902	)	$	6,254	(291		)
Interest rate swaps	$	50	2,900		23,900	100		$	26,950	(8		)
Payer swaptions	$	850	4,450		—	(2,050	)	$	3,250	(58		)
Receiver Swaptions	$	—	250		—	(250	)	$	—	(1		)
Short sales of U.S. Treasury securities	$	250	11,974		—	(11,759	)	$	465	(92		)
Put Options	$	—	(200	)	—	200		$	—	1
U.S. Treasury futures - long	$	—	400		—	(50	)	$	350	2
Markit IOS total return swaps - long	$	—	1,154		—	(1,089	)	$	65	(6		)
Markit IOS total return swaps - short	$	—	636		—	(313	)	$	323	17
										$	(317	)

______________________

Schedule Of Outstanding Not Designated As Hedging Instruments [Table Text Block]



	Three Months Ended September 30, 2012
Derivatives Not Designated as Hedging Instruments	Notional Amount as of June 30, 2012		Additions	Settlement, Termination, Expiration or Exercise		Notional Amount as of September 30, 2012		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	7,447	36,956	(26,234	)	$	18,169	$	222
Sale of TBA and forward settling agency securities	$	10,851	53,318	(49,774	)	$	14,395	(173		)
Interest rate swaps	$	48,550	3,450	(3,150	)	$	48,850	(438		)
Payer swaptions	$	8,800	2,000	(2,250	)	$	8,550	(25		)
Short sales of U.S. Treasury securities	$	1,250	11,550	(5,505	)	$	7,295	(15		)
U.S. Treasury futures - short	$	1,919	—	(1,919	)	$	—	(27		)
Markit IOS total return swaps - long	$	37	—	(37	)	$	—	—
Markit IOS total return swaps - short	$	181	—	(181	)	$	—	—
								$	(456	)

________________________________


1.	Excludes a gain of $20 million from interest-only and principal-only securities and a loss of $24 million from debt of consolidated VIEs re-measured at fair value through earnings recognized in gain (loss) on derivative instruments and other securities, net in our consolidated statement of comprehensive income for the three months ended September 30, 2012.



	Three Months Ended September 30, 2011
Derivatives Not Designated as Hedging Instruments	Notional Amount as of June 30, 2011		Additions	Additions Due to Hedge De-Designations	Settlement, Termination, Expiration or Exercise		Notional Amount as of September 30, 2011		Amount of Gain/(Loss) Recognized in Income on Derivatives⁽¹⁾
Purchase of TBA and forward settling agency securities	$	3,432	19,881	—	(17,877	)	$	5,436	$	73
Sale of TBA and forward settling agency securities	$	4,282	37,867	—	(35,895	)	$	6,254	(146		)
Interest rate swaps	$	150	2,900	23,900	—		$	26,950	(3		)
Payer swaptions	$	4,050	250	—	(1,050	)	$	3,250	(33		)
Short sales of U.S. Treasury securities	$	1,464	3,450	—	(4,449	)	$	465	(92		)
US Treasury futures - long	$	—	350	—	—		$	350	2
Markit IOS total return swaps - long	$	683	65	—	(683	)	$	65	(19		)
Markit IOS total return swaps - short	$	309	323	—	(309	)	$	323	20
									$	(198	)

______________________

Not Designated as Hedging Instrument [Member]

Derivative [Line Items]

Schedule Of Interest Rate Swap Agreement By Remaining Maturity

The following tables summarize our interest rate swap agreements outstanding as of September 30, 2012 and December 31, 2011 (dollars in millions).



	September 30, 2012
Payer Interest Rate Swaps Not Designated as Hedging Instruments⁽¹⁾	Notional Amount		Average Fixed Pay Rate		Average Receive Rate		Net Estimated Fair Value			Average Maturity (Years)
Three years or less	$	17,150	1.15	%	0.30	%	$	(308	)	2.0
Greater than 3 years and less than/equal to 5 years	19,400		1.55	%	0.35	%	(767		)	4.2
Greater than 5 years and less than/equal to 7 years	7,100		1.41	%	0.43	%	(203		)	6.1
Greater than 7 years and less than/equal to 10 years	5,200		1.89	%	0.45	%	(158		)	9.4
Total Payer Interest Rate Swaps	$	48,850	1.43	%	0.35	%	$	(1,436	)	4.3

________________________


1.	Amounts include forward starting swaps of $3.1 billion ranging up to six months from September 30, 2012.



	December 31, 2011
Payer Interest Rate Swaps Not Designated as Hedging Instruments⁽¹⁾	Notional Amount		Average Fixed Pay Rate		Average Receive Rate		Net Estimated Fair Value			Average Maturity (Years)
Three years or less	$	11,350	1.22	%	0.30	%	$	(148	)	2.1
Greater than 3 years and less than/equal to 5 years	16,700		1.77	%	0.35	%	(607		)	3.9
Greater than 5 years and less than/equal to 7 years	950		1.56	%	0.57	%	(9		)	5.7
Greater than 7 years and less than/equal to 10 years	1,250		1.99	%	0.55	%	(18		)	8.2
Total Payer Interest Rate Swaps	$	30,250	1.57	%	0.35	%	$	(782	)	3.5

________________________


1.	Amounts include forward starting swaps of $2.6 billion ranging up to five months from December 31, 2011.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following table provides a summary of our assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2012 and December 31, 2011 (dollars in millions):



	Fair Value Hierarchy
	Level 1		Level 2		Level 3
September 30, 2012
Assets:
Agency securities	$	—	$	89,640	$	—
Interest rate swaps	—		6		—
Other derivative instruments	—		286		—
Total	$	—	$	89,932	$	—
Liabilities:
Debt of consolidated VIEs	$	—	$	968	$	—
Obligation to return U.S. Treasury securities borrowed under reverse repurchase agreements	7,265		—		—
Interest rate swaps	—		1,442		—
Other derivative instruments	—		120		—
Total	$	7,265	$	2,530	$	—

December 31, 2011
Assets:
Agency securities	$	—	$	54,683	$	—
U.S. Treasury securities	101		—		—
Interest rate swaps	—		13		—
Other derivative instruments	—		69		—
Total	$	101	$	54,765	$	—
Liabilities:
Obligation to return U.S. Treasury securities borrowed under reverse repurchase agreements	$	899	$	—	$	—
U.S. Treasury futures	14		—		—
Interest rate swaps	—		795		—
Other derivative instruments	—		44		—
Total	$	913	$	839	$	—

Organization (Details)	9 Months Ended
Organization (Details)	Sep. 30, 2012
Organization [Abstract]
Required distribution of taxable net income on a annual basis	90.00%

Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unrealized (loss) gain on derivative instruments, net	$ 51	$ 52	$ 52	$ (512)	$ 155	$ (704)
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate	100.00%				100.00%
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate	300.00%				300.00%
Interest Rate Swap [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Derivative, Average Remaining Maturity					10 years

- Definition

Net of tax amount, before reclassification adjustments, of the change in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Also includes an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=20435746&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e637-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6441202&loc=d3e80720-113993

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 130
-Paragraph 17, 20
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 130
-Paragraph 121
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 46
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 130
-Paragraph 24
-Subparagraph b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 38
-Subparagraph c(3)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Investment Securities (Narrative) (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
Investment Securities (Narrative) (Details) $ in Millions	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2012 USD ($) years	Sep. 30, 2011 USD ($)	Dec. 31, 2011 USD ($) years
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Unamortized Premium	$ 4,415		$ 4,415		$ 2,428
Future Prepayment Rate Assumption Of Investment Portfolio			14.00%
Weighted average life of interest-only securities			4.8		3.0
Weighted average life of principal-only securities \| years			5.6		2.6
Prepayment rate over remaining life of aggregate investment portfolio					14.00%
Unrealized gain on interest-only and principal-only securities	(20)	$ (28)	$ (19)	$ (24)
Fair value of CMO securities and interest-only strips	766		766		$ 426
Fair value of CMO securities and interest-only securities including net asset value	1,400		1,400		429
CMO and Interest Only, Pricincipal Only Securities, Maximum Loss Exposure			375		155
Fair value of agency securities collaterizing debt issued by securitization trust	1,600		1,600		58
Principal balance of agency securities collaterizing debt issued by securitization trust	1,500		1,500		55
Other Long-term Debt	1,008		1,008		$ 54
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized Gain (Loss) on Derivatives	$ (24)		$ (32)

Investment Securities (Summary of Investment in Agency Security) (Details) - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Dec. 31, 2011

Unrealized Gain On Derivative Instrument And Trading Securities

$ 20

$ 28

$ 19

$ 24

Unamortized premium

4,415

$ 2,428

Amortized cost

86,282

53,503

Total agency MBS, at fair value

$ 89,640

$ 54,683

Weighted average coupon

3.77%

^[1]

3.77%

^[1]

4.23%

^[2]

Weighted average yield

2.61%

^[3]

2.61%

^[3]

3.07%

Weighted average yield for the year ended

2.55%

^[3]

2.82%

^[3]

3.19%

Unamortized principal balance of interest-only strips

$ 1,800

$ 1,100

Unamortized principal balance of principal-only strips

$ 309

$ 40

Weighted average contractual interest rate of interest only strips

5.70%

0.00%

Prepayment rate over remaining life of aggregate investment portfolio

14.00%

Average prepayment rate based on forward rate assumption

14.00%

Average reset rate for adjustable rate securities

2.67%

2.71%

Average underlying index rate on agency securities based on current spot rate

0.96%

0.94%

Average Margin on agency securities

1.71%

1.77%

Fannie Mae [Member]

Total agency MBS, at fair value

$ 70,357

$ 39,689

Weighted average coupon

3.74%

^[1]

3.74%

^[1]

4.18%

^[2]

Weighted average yield

2.56%

^[3]

2.56%

^[3]

3.03%

Weighted average yield for the year ended

2.53%

^[3]

2.82%

^[3]

3.19%

Freddie Mac [Member]

Total agency MBS, at fair value

$ 19,005

$ 14,721

Weighted average coupon

3.88%

^[1]

3.88%

^[1]

4.39%

^[2]

Weighted average yield

2.82%

^[3]

2.82%

^[3]

3.20%

Weighted average yield for the year ended

2.62%

^[3]

2.85%

^[3]

3.20%

Ginnie Mae [Member]

Total agency MBS, at fair value

$ 278

$ 273

Weighted average coupon

3.78%

^[1]

3.78%

^[1]

3.74%

^[2]

Weighted average yield

1.60%

^[3]

1.60%

^[3]

1.71%

Weighted average yield for the year ended

1.54%

^[3]

1.64%

^[3]

2.05%

Available-for-sale Securities [Member]

Agency MBS, par

$ 82,124

$ 51,226

Unamortized premium

4,158

2,277

Amortized cost

86,282

53,503

Gross unrealized gains

2,784

1,007

Gross unrealized losses

(1)

(6)

Total available-for-sale agency MBS, at fair value

89,065

54,504

Available-for-sale Securities [Member] | Fannie Mae [Member]

Agency MBS, par

64,352

37,232

Unamortized premium

3,319

1,659

Amortized cost

67,671

38,891

Gross unrealized gains

2,161

680

Gross unrealized losses

(1)

(4)

Total available-for-sale agency MBS, at fair value

69,831

39,567

Available-for-sale Securities [Member] | Freddie Mac [Member]

Agency MBS, par

17,512

13,736

Unamortized premium

827

606

Amortized cost

18,339

14,342

Gross unrealized gains

617

324

Gross unrealized losses

(2)

Total available-for-sale agency MBS, at fair value

18,956

14,664

Available-for-sale Securities [Member] | Ginnie Mae [Member]

Agency MBS, par

260

258

Unamortized premium

Amortized cost

272

270

Gross unrealized gains

Gross unrealized losses

Total available-for-sale agency MBS, at fair value

278

273

Agency MBS remeasured at fair value through earnings [Member]

Interest-only and principal-only strips, amortized cost

568

191

^[4]

Gross unrealized gains

Gross unrealized losses

(24)

(21)

Total agency MBS remeasured at fair value through earnings, at fair value

575

179

Agency MBS remeasured at fair value through earnings [Member] | Fannie Mae [Member]

Interest-only and principal-only strips, amortized cost

508

124

^[4]

Gross unrealized gains

Gross unrealized losses

(12)

(8)

Total agency MBS remeasured at fair value through earnings, at fair value

526

122

Agency MBS remeasured at fair value through earnings [Member] | Freddie Mac [Member]

Interest-only and principal-only strips, amortized cost

^[4]

Gross unrealized gains

Gross unrealized losses

(12)

(13)

Total agency MBS remeasured at fair value through earnings, at fair value

Agency MBS remeasured at fair value through earnings [Member] | Ginnie Mae [Member]

Interest-only and principal-only strips, amortized cost

^[4]

Gross unrealized gains

Gross unrealized losses

Total agency MBS remeasured at fair value through earnings, at fair value

$ 0

Debt Securities [Member]

Unrealized Gain (Loss) on Derivatives

$ (24)

$ (32)

[1]	Interest-only agency MBS strips represent the right to receive a specified portion of the contractual interest flows of the underlying unamortized principal balance (“UPB” or “par value”) of specific agency CMO securities. Principal-only agency MBS strips represent the right to receive contractual principal flows of the UPB of specific agency CMO securities. The UPB of our interest-only agency MBS strips was $1.8 billion and the weighted average contractual interest we are entitled to receive was 5.70% of this amount as of September 30, 2012. The par value of our principal-only agency MBS strips was $309 million as of September 30, 2012.
[2]	The weighted average coupon includes the interest cash flows from our interest-only securities taken together with the interest cash flows from our fixed-rate, adjustable-rate and CMO securities as a percentage of the par value of our agency securities (excluding the UPB of our interest-only securities) as of December 31, 2011.
[3]	Incorporates a weighted average future constant prepayment rate assumption of 14% based on forward rates as of September 30, 2012 and a weighted average reset rate for adjustable rate securities of 2.67%, which is equal to a weighted average underlying index rate of 0.96% based on the current spot rate in effect as of the date we acquired the securities and a weighted average margin of 1.71%.
[4]	The UPB of our interest-only securities was $1.1 billion and the weighted average contractual interest we are entitled to receive was 5.52% of this amount as of December 31, 2011. The par value of our principal-only agency MBS strips was $40 million as of December 31, 2011

Investment Securities (Components Of Investment Securities) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
CMO and Interest Only, Pricincipal Only Securities, Maximum Loss Exposure	$ 375	$ 155
Prepayment Rate Of Remaining Life Of Investment Portfolio		14.00%
Amortized cost	86,850	$ 53,694
Gross unrealized gains	2,815	1,016
Gross unrealized losses	(25)	(27)
Available-for-sale Securities, Fair Value Disclosure	89,065	54,504
Total agency MBS, at fair value	89,640	54,683
Total Agency Securities	89,640	54,683
Fixed-Rate [Member]
Amortized cost	85,136	50,535
Gross unrealized gains	2,747	952
Gross unrealized losses	(1)	(4)
Available-for-sale Securities, Fair Value Disclosure	87,882	51,483
Adjustable-Rate [Member]
Amortized cost	960	2,725
Gross unrealized gains	32	51
Gross unrealized losses	0	(2)
Available-for-sale Securities, Fair Value Disclosure	992	2,774
CMO [Member]
Amortized cost	186	243
Gross unrealized gains	5	4
Gross unrealized losses	0	0
Available-for-sale Securities, Fair Value Disclosure	191	247
Interest-Only-Strip [Member]
Amortized cost		191
Gross unrealized gains		9
Gross unrealized losses		(21)
Fair Value		$ 179
Interest-Only And Principal-Only Securities [Member]
Amortized cost	568
Gross unrealized gains	31
Gross unrealized losses	(24)
Fair Value	$ 575

Investment Securities (Summary Of Agency Securities Estimated Weighted Average Life Classifications) (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2012 USD ($) years	Dec. 31, 2011 USD ($) years
Weighted Average Life of Interest Only Securities	4.8	3.0
Agency securities classified as available for sale, Fair value	$ 89,065	$ 54,504
Agency securities classified as available for sale, Amortized cost	$ 86,282	$ 53,503
Weighted average coupon	3.66%	4.11%
Weighted Average Life Of Principal Only Securities \| years	5.6	2.6
Less Than or Equal to One Year [Member]
Available For Sale Securities Weighted Average Life Fair Value	$ 0	$ 214
Available For Sale Securities Weighted Average Life Amortized Cost	$ 0	$ 210
Weighted average coupon	0.00%	4.61%
Greater Than One Year and Less Than or Equal to Three Years [Member]
Available For Sale Securities Weighted Average Life Fair Value	$ 9,902	$ 3,392
Available For Sale Securities Weighted Average Life Amortized Cost	$ 9,656	$ 3,338
Weighted average coupon	3.17%	4.38%
Greater Than Three Years and Less Than or Equal to Five Years [Member]
Available For Sale Securities Weighted Average Life Fair Value	$ 39,737	$ 26,168
Available For Sale Securities Weighted Average Life Amortized Cost	$ 38,442	$ 25,616
Weighted average coupon	3.66%	3.99%
Greater Than Five Years [Member]
Available For Sale Securities Weighted Average Life Fair Value	$ 38,832	$ 24,710
Available For Sale Securities Weighted Average Life Amortized Cost	$ 37,600	$ 24,320
Weighted average coupon	3.80%	4.19%
Greater Than Ten Years [Member]
Available For Sale Securities Weighted Average Life Fair Value	$ 594	$ 20
Available For Sale Securities Weighted Average Life Amortized Cost	$ 584	$ 19
Weighted average coupon	3.55%	5.02%

Investment Securities (Summary Of Changes In Accumulated OCI For Available-For-Sale Security) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Unrealized gain (loss) on available-for-sale securities, net	$ 1,190	$ 689	$ (106)	$ 536	$ 1,773	$ 815
Agency Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning OCI Balance	1,585		$ 1,002	251	1,002	(28)
Unrealized gain (loss) on available-for-sale securities, net	1,400			802	2,616	1,178
Reversal of prior Period Unrealized (Gains) and Losses, Net on Realization	210			266	843	363
Ending OCI Balance	$ 2,775	$ 1,585		$ 787	$ 2,775	$ 787

- Definition

Net of tax amount of unrealized holding gain (loss) before reclassification adjustments and transfers on available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=20435746&loc=SL7669646-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e637-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 13
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 130
-Paragraph 17, 22
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 130
-Paragraph 24
-Subparagraph b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 38
-Subparagraph c(3)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Investment Securities (Summary Of Continuous Unrealized Loss Positions Of Available-For-Sale Security) (Details) - Accumulated Other Comprehensive Income (Loss) [Member] - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Unrealized Loss Position For - Estimated Fair Value - Less than 12 Months	$ 436	$ 1,135
Unrealized Loss Position For - Unrealized Loss - Less than 12 Months	(1)	(6)
Unrealized Loss Position For - Estimated Fair Value - 12 Months or More	0	0
Unrealized Loss Position For - Unrealized Loss - 12 Months or More	0	0
Unrealized Loss Position For - Estimated Fair Value - Total	436	1,135
Unrealized Loss Position For - Unrealized Loss - Total	$ 1	$ 6

Investment Securities (Summary Of Net Gain From Sale Of Agency Securities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Unrealized Gain On Derivative Instrument And Trading Securities	$ 20	$ 28	$ 19	$ 24
Total Agency Securities	$ 89,640		89,640		$ 54,683
Document Period End Date	Sep. 30, 2012
Proceeds from agency MBS sold			(2,545)	(3,791)
Gain (Loss) on Sales of Mortgage Backed Securities (MBS)	$ 210	263	843	361
Agency Securities Amortized Cost	86,850		86,850		53,694
Agency Securities [Member]
Agency MBS sold, at cost	(10,172)	14,046	45,258	26,429
Proceeds from agency MBS sold	(10,382)	(14,309)	(46,101)	(26,790)
Gain (Loss) on Sales of Mortgage Backed Securities (MBS)	210	263	843	361
Gross gains on sale of agency MBS	210	268	855	377
Gross losses on sale of agency MBS	0	$ 5	12	16
Interest Only And Principal Only Strip [Member]
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net			0	$ 3
Freddie Mac [Member]
Total Agency Securities	19,005		19,005		14,721
Available-for-sale Securities [Member]
Available For Sale Securities Par	82,124		82,124		51,226
Available-for-sale Securities [Member] \| Freddie Mac [Member]
Available For Sale Securities Par	$ 17,512		$ 17,512		$ 13,736

Investment Securities (Summary Of Agency Securities Pledged As Collateral Under Repurchase, Other Debt, Derivative And Prime Broker Agreements) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Fair value	$ 83,600		$ 83,600		$ 50,667
Accrued interest on pledged agency securities	243		243		163
Gain on sale of agency securities, net	210	$ 263	843	$ 361
Restricted Cash and Cash Equivalents	369		369		336
Total Fair Value of Agency Securities Pledged and Accrued Interest	87,298		87,298		51,644
Repurchase Agreements [Member]
Fair value	83,654		83,654		50,255
Accrued interest on pledged agency securities	234		234		161
Total Fair Value of Agency Securities Pledged and Accrued Interest	83,888		83,888		50,517
Repurchase Agreements [Member] \| Treasuries [Member]
Fair value	0		0		101
Under Repurchase Agreements [Member]
Fair value	1,620		1,620		58
Accrued interest on pledged agency securities	5		5		0
Total Fair Value of Agency Securities Pledged and Accrued Interest	1,625		1,625		58
Under Derivative Agreements [Member]
Fair value	1,255		1,255		644
Accrued interest on pledged agency securities	4		4		2
Total Fair Value of Agency Securities Pledged and Accrued Interest	1,628		1,628		982
Under Prime Broker Agreements [Member] \| Fannie Mae [Member]
Fair value	157		157		87
Accrued interest on pledged agency securities	0		0		0
Total Fair Value of Agency Securities Pledged and Accrued Interest	157		157		87
Includes Sold But Not Yet Settled Securities [Member]
Fair value	86,686		86,686		$ 51,044
Agency Securities [Member]
Cost Of Sale Of Available For Sale Securities	(10,172)	14,046	45,258	26,429
Gain on sale of agency securities, net	$ 210	$ 263	$ 843	$ 361

Investment Securities (Summary Of Agency Securities Pledged As Collateral Under Repurchase Agreements By Remaining Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Fair Value Of CMO Securities Directly Held	$ 766	$ 426
Fair value	85,274	50,313
Amortized cost	82,591	49,342
Accrued Interest on pledged agency securities	239	161
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	0	101
Available-for-sale Securities Pledged as Collateral	83,600	50,667
Security Owned and Pledged as Collateral, Fair Value	85,274	50,414
All securities pledged collateral at amortized cost	82,591	49,443
30 Days or Less [Member]
Fair value	30,861	19,772
Amortized cost	29,867	19,361
Accrued Interest on pledged agency securities	86	63
Maturity 31 To 59 Days [Member]
Fair value	17,739	16,964
Amortized cost	17,134	16,648
Accrued Interest on pledged agency securities	51	55
Maturity 60 To 90 Days [Member]
Fair value	17,822	8,337
Amortized cost	17,242	8,179
Accrued Interest on pledged agency securities	50	26
Greater than 90 Days [Member]
Fair value	18,852	5,240
Amortized cost	18,348	5,154
Accrued Interest on pledged agency securities	52	17
Treasuries [Member]
Amortized cost	0	101
Repurchase Agreements [Member]
Available-for-sale Securities Pledged as Collateral	83,654	50,255
Repurchase Agreements [Member] \| Treasuries [Member]
Available-for-sale Securities Pledged as Collateral	$ 0	$ 101

Repurchase Agreements And Other Debt (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2012 USD ($) years	Mar. 31, 2012	Dec. 31, 2011 USD ($)
Debt Instrument [Line Items]
Weighted Average Life of Other Debt \| years	3.8
Risk of repurchase agreement to stockholders equity		4.00%
Other Long-term Debt	$ 1,008		$ 54
Debt Instrument, Face Amount	979
other debt net of discounts	$ 976
Debt Instrument, Description of Variable Rate Basis, LIBOR	LIBOR
Spread Over LIBOR	42

Repurchase Agreements And Other Debt (Repurchase Arrangements And Weighted Average Interest Rates Classified By Original Maturities) (Details) - USD ($)	Sep. 30, 2012	Dec. 31, 2011
Debt Instrument, Face Amount	$ 979,000,000
Borrowings Outstanding	$ 79,254,000,000	$ 47,681,000,000
Average Interest Rate	0.46%	0.40%
Weighted Average Days to Maturity	89	51
other debt net of discounts	$ 976,000,000
1 Month or Less
Borrowings Outstanding	$ 4,724,000,000	$ 2,558,000,000
Average Interest Rate	0.43%	0.43%
Weighted Average Days to Maturity	12	10
thirty one to ninety [Member]
Borrowings Outstanding	$ 31,253,000,000	$ 24,518,000,000
Average Interest Rate	0.43%	0.39%
Weighted Average Days to Maturity	37	32
120 to 180 days [Member]
Borrowings Outstanding	$ 25,571,000,000	$ 16,475,000,000
Average Interest Rate	0.45%	0.37%
Weighted Average Days to Maturity	72	53
210 to 270 days [Member]
Borrowings Outstanding	$ 8,641,000,000	$ 2,423,000,000
Average Interest Rate	0.49%	0.45%
Weighted Average Days to Maturity	92	141
300 to 360 days [Member]
Borrowings Outstanding	$ 7,547,000,000	$ 1,006,000,000
Average Interest Rate	0.57%	0.53%
Weighted Average Days to Maturity	266	244
390 to 720 days [Member]
Borrowings Outstanding	$ 693,000,000	$ 600,000,000
Average Interest Rate	0.67%	0.51%
Weighted Average Days to Maturity	613	268
750 to 1080 days [Member]
Borrowings Outstanding	$ 825,000,000
Average Interest Rate	0.72%
Weighted Average Days to Maturity	992
Mortgage Backed Securities, Other [Member]
Borrowings Outstanding	$ 79,254,000,000	$ 47,580,000,000
Average Interest Rate	0.46%	0.40%
Weighted Average Days to Maturity	89	51
Treasuries [Member]
Borrowings Outstanding	$ 0	$ 101,000,000
Average Interest Rate	0.00%	0.40%
Weighted Average Days to Maturity	0	1
Other Debt Obligations [Member]
Debt Instrument, Face Amount	$ 939,000,000
other debt net of discounts	$ 936,000,000

Derivative and Other Hedging Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011
Gain On Interest Only Securities Remeasured at Fair Value Through Earnings			$ 19
Fair Value of Derivative Instruments	$ 109		109			$ 13
Obligation to return securities borrowed under reverse repurchase agreements, at fair value	7,265		7,265			$ 899
Proceeds from sales of treasury securities			7,200		$ 880
Gain on interest only securities remeasured at fair value through earnings	20	$ (28)		$ (24)
Loss on interest only securities remeasured at fair value through earnings	20	(28)		(24)
Loss on cash flow hedge ineffectiveness		1		(2)
Gain on trading securities	(20)	(28)	(19)	(24)
Restricted Cash Pledged As Collateral	332		332
Unrealized Gain (Loss) On Derivative Instrument And Trading Securities	(460)	$ (222)	(1,442)	$ (310)
Interest Rate Contract [Member]
Fair value of interest rate swap, liability position	1,400		1,400
Agency securities, pledged as collateral against interest rate swap	1,300		1,300
Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member]
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge	$ 536		536
Deferred gain loss discontinued interest rate swap expected to be reclassified from OCI to interest expense next twelve months			$ 194

Derivative and Other Hedging Instruments (Remaining Interest Rate Swap Term) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Unrealized (loss) gain on derivative instruments, net	$ 51	$ 52	$ 52	$ (512)	$ 155	$ (704)
Notional Amount				$ 0		$ 0	$ 0	$ 22,000	$ 6,450
Notional amount of forward starting swaps	3,774				$ 3,774		$ (103)
Remaining interest rate swap term, maximum					6 months		5 months
Not Designated as Hedging Instrument [Member]
Notional Amount	$ 48,850				$ 48,850		$ 30,250
Average Maturity (Years)					4 years 3 months 18 days		3 years 6 months
Average Fixed Pay Rate	1.43%				1.43%		1.57%
Average Receive Rate	0.35%				0.35%		0.35%
Net Estimated Fair Value	$ (1,436)				$ (1,436)		$ (782)
Greater Than One Year and Less Than or Equal to Three Years [Member]
Notional Amount	$ 17,150				$ 17,150		$ 11,350
Average Maturity (Years)					2 years		2 years 1 month 6 days
Average Fixed Pay Rate	1.15%				1.15%		1.22%
Average Receive Rate	0.30%				0.30%		0.30%
Net Estimated Fair Value	$ (308)				$ (308)		$ (148)
Greater Than Three Years and Less Than or Equal to Five Years [Member]
Notional Amount	$ 19,400				$ 19,400		$ 16,700
Average Maturity (Years)					4 years 2 months 12 days		3 years 10 months 24 days
Average Fixed Pay Rate	1.55%				1.55%		1.77%
Average Receive Rate	0.35%				0.35%		0.35%
Net Estimated Fair Value	$ (767)				$ (767)		$ (607)
Greater Than Five Years and Less than or Equal to Seven Years [Member]
Notional Amount	$ 7,100				$ 7,100		$ 950
Average Maturity (Years)					6 years 1 month 6 days		5 years 8 months 12 days
Average Fixed Pay Rate	1.41%				1.41%		1.56%
Average Receive Rate	0.43%				0.43%		0.57%
Net Estimated Fair Value	$ (203)				$ (203)		$ (9)
Greater Than Seven Years and Less than or Equal to Ten Years [Member]
Notional Amount	$ 5,200				$ 5,200		$ 1,250
Average Maturity (Years)					9 years 4 months 24 days		8 years 2 months 12 days
Average Fixed Pay Rate	1.89%				1.89%		1.99%
Average Receive Rate	0.45%				0.45%		0.55%
Net Estimated Fair Value	$ (158)				$ (158)		$ (18)
Interest Rate Swap [Member]
Average Maturity (Years)					10 years
Interest Rate Swap [Member]
Notional amount of forward starting swaps	$ 3,100				$ 3,100		$ 2,600

Derivative and Other Hedging Instruments (Summary Of Outstanding Interest Rate Swaps Designated As Hedging Instruments) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Derivative Asset, Fair Value, Net [Abstract]
Notional Amount	$ 0	$ 0	$ 0	$ 22,000	$ 6,450
Additions	2,100	17,900
Terminations	(200)	(450)
Hedge De-Designation	$ 23,900	$ 23,900

Derivative and Other Hedging Instruments (Effect Of Interest Rate Swaps Designated As Hedges) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivatives, Fair Value [Line Items]
Net Periodic Interest Rate Costs on Swaps	$ 125		$ 330
Amount of Gain or (Loss) Recognized in OCI (Effective Portion)		$ (512)		$ (707)
Amount of Gain or (Loss) Reclassified from OCI into Earnings (Effective Portion)		(71)		(140)
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net		(1)		(2)
Loss on cash flow hedge ineffectiveness		$ 1		$ (2)
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	$ 74		$ 175

- Definition

The effective portion of gain reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References + Details

Derivative and Other Hedging Instruments (Summary Of Outstanding Forward Contracts Designated As Hedging Instruments) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2012 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)
Net Periodic Interest Rate Costs on Swaps	$ 125	$ 330
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	$ 74	$ 175
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Beginning Notional Amount			$ 245
Additions			0
Settlement /Expirations			(245)
Ending Notional Amount			0
Fair Value as of Period End			$ 0
Average Maturity as of Period End (Months)			0

- Definition

The effective portion of gain reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References + Details

Derivative and Other Hedging Instruments (Effect of Forward Contracts Designated as Hedges) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Amount of Gain or (Loss) Recognized in OCI (Effective Portion)				$ (512)		$ (707)
Amount of Gain or (Loss) Reclassified from OCI into Earnings (Effective Portion)				(71)		(140)
Amount of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)				(1)		(2)
Unrealized (loss) gain on derivative instruments, net	$ 51	$ 52	$ 52	$ (512)	$ 155	(704)
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Amount of Gain or (Loss) Recognized in OCI (Effective Portion)						0
Amount of Gain or (Loss) Reclassified from OCI into Earnings (Effective Portion)						(3)
Amount of Gain or (Loss) Recognized in Earnings (Ineffective Portion and Amount Excluded from Effectiveness Testing)						$ 0

- Definition

+ References

+ Details

Derivative and Other Hedging Instruments (Summary of Long and Short Position of Derivative Instruments) (Details) - USD ($)
$ in Millions

Sep. 30, 2012

Dec. 31, 2011

Notional Amount

$ 3,774

$ (103)

Fair Value of Derivative Instruments

109

TBA securities Fifteen Year and Thirty Year Securities [Member]

Notional Amount

^[1]

4,634

(615)

Fair Value of Derivative Instruments

^[1]

107

TBA securities Fifteen Year and Thirty Year Securities [Member] | Purchase [Member]

Notional Amount

17,844

3,188

Fair Value of Derivative Instruments

161

TBA securities Fifteen Year and Thirty Year Securities [Member] | Sale [Member]

Notional Amount

(13,210)

(3,803)

Fair Value of Derivative Instruments

(54)

(41)

Forward settling securities Twenty Year Securities and ARMs [Member]

Notional Amount

^[2]

(860)

512

Fair Value of Derivative Instruments

^[2]

Forward settling securities Twenty Year Securities and ARMs [Member] | Purchase [Member]

Notional Amount

325

512

Fair Value of Derivative Instruments

Forward settling securities Twenty Year Securities and ARMs [Member] | Sale [Member]

Notional Amount

(1,185)

Fair Value of Derivative Instruments

$ (3)

$ 0

[1]	Includes 15-year and 30-year TBA securities of varying coupons
[2]	Includes 20-year and 30-year fixed securities of varying coupons

Derivative and Other Hedging Instruments (Summary Of Outstanding Interest Rate Swaps Agreements Not Designated As Hedges) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2010
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net		$ 1		$ (2)
Securitites borrowed under reverse purchase agreements, fair value	$ 7,265		$ 7,265		$ 899
Notional Amount of Interest Rate Derivatives		0		0	0		$ 22,000	$ 6,450
Notional Amount		0		0	0		22,000	6,450
Additions Of Interest Rate Cash Flow Hedge Derivatives		2,100		17,900
Terminations Of Interest Rate Cash Flow Hedge Derivatives		(200)		(450)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(456)	(198)	(1,428)	(317)
Hedge De-Designation Of Interest Rate Cash Flow Hedge Derivatives		(23,900)		(23,900)
Payer Interest Rate Swaps [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	3,450	2,900	23,300	2,900
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		23,900		23,900
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(3,150)	0	(4,700)	100
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	48,850	26,950	48,850	26,950	30,250	$ 48,550	150	50
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(438)	(3)	(1,067)	(8)
Payer Swaption [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	2,000	250	12,150	4,450
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		0		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(2,250)	(1,050)	(6,800)	(2,050)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	8,550	3,250	8,550	3,250	3,200	8,800	4,050	850
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(25)	(33)	(96)	(58)
Treasury Futures [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	0		3,838	400
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations				0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(1,919)		(4,621)	(50)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	0	350	0	350	783	1,919		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(27)		(91)	2
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	36,956	19,881	90,498	42,222
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		0		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(26,234)	(17,877)	(76,028)	(37,298)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	18,169	5,436	18,169	5,436	3,699	7,447	3,432	512
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	222	73	343	119
Receiver Swaption [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period				250
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations				0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period				(250)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments		0		0				0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net				(1)
Markit IOS Total Return Swaps - Long [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	0	65	0	1,154
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		0		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(37)	(683)	(41)	(1,089)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments		65		65	41	37	683	0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0	(19)	0	(6)
Sale Of TBA And Forward Settling Agency Securities [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	53,318	37,867	131,030	88,795
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		0		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(49,774)	(35,895)	(120,438)	(83,902)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	14,395	6,254	14,395	6,254	3,803	10,851	4,282	1,361
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(173)	(146)	(402)	(291)
Short Sales Of U S Government Securities [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	11,550	3,450	30,480	11,974
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		0		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(5,505)	(4,449)	(24,065)	(11,759)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	7,295	465	7,295	465	880	1,250	1,464	250
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(15)	(92)	(115)	(92)
Markit IOS Total Return Swaps - Short [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	0	323	0	636
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		0		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(181)	(309)	(206)	(313)
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	0	323	0	323	206	$ 181	309	0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0	20	0	17
US Treasury Securities [Member]
Trading Securities, Realized Gain (Loss)		5		33
Derivative liabilities, at fair value [Member]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(1,562)		(1,562)		(853)
Derivative liabilities, at fair value [Member] \| Payer Interest Rate Swaps [Member]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(1,442)		(1,442)		(795)
Derivative liabilities, at fair value [Member] \| Treasury Futures [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0		0		(14)
Derivative liabilities, at fair value [Member] \| Purchases Of TBAs And Forward Settling Agency Securities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	(20)		(20)		0
Derivative liabilities, at fair value [Member] \| Sale Of TBA And Forward Settling Agency Securities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(100)		(100)		(44)
Derivative assets, at fair value [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	292		292		82
Derivative assets, at fair value [Member] \| Payer Interest Rate Swaps [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value					13
Derivative assets, at fair value [Member] \| Payer Swaption [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	57		57		11
Derivative assets, at fair value [Member] \| Purchases Of TBAs And Forward Settling Agency Securities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	186		186		54
Derivative assets, at fair value [Member] \| Markit IOS Total Return Swaps - Long [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0		0		1
Derivative assets, at fair value [Member] \| Sale Of TBA And Forward Settling Agency Securities [Member]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	43		43		3
Put Option [Member]
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period		350		(200)
Notional Amount Of Derivatives Not Designated As Hedging Instruments additions due to Hedge De-Designations		0		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period		0		200
Notional Amount of Other Derivatives Not Designated as Hedging Instruments		0		0			$ 0	$ 0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		$ 2		$ 1
Greater Than One Year and Less Than or Equal to Three Years [Member]
Notional Amount of Interest Rate Derivatives	17,150		17,150		11,350
Notional Amount	$ 17,150		$ 17,150		$ 11,350
Average Fixed Pay Rate	1.15%		1.15%		1.22%
Average Receive Rate	0.30%		0.30%		0.30%
Net Estimated Fair Value	$ (308)		$ (308)		$ (148)
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate	0.30%		0.30%		0.30%
Derivative, Average Remaining Maturity			2 years		2 years 1 month 6 days
Greater Than Three Years and Less Than or Equal to Five Years [Member]
Notional Amount of Interest Rate Derivatives	$ 19,400		$ 19,400		$ 16,700
Notional Amount	$ 19,400		$ 19,400		$ 16,700
Average Fixed Pay Rate	1.55%		1.55%		1.77%
Average Receive Rate	0.35%		0.35%		0.35%
Net Estimated Fair Value	$ (767)		$ (767)		$ (607)
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate	0.35%		0.35%		0.35%
Derivative, Average Remaining Maturity			4 years 2 months 12 days		3 years 10 months 24 days
Greater Than Five Years and Less than or Equal to Seven Years [Member]
Notional Amount of Interest Rate Derivatives	$ 7,100		$ 7,100		$ 950
Notional Amount	$ 7,100		$ 7,100		$ 950
Average Fixed Pay Rate	1.41%		1.41%		1.56%
Average Receive Rate	0.43%		0.43%		0.57%
Net Estimated Fair Value	$ (203)		$ (203)		$ (9)
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate	0.43%		0.43%		0.57%
Derivative, Average Remaining Maturity			6 years 1 month 6 days		5 years 8 months 12 days
Greater Than Seven Years and Less than or Equal to Ten Years [Member]
Notional Amount of Interest Rate Derivatives	$ 5,200		$ 5,200		$ 1,250
Notional Amount	$ 5,200		$ 5,200		$ 1,250
Average Fixed Pay Rate	1.89%		1.89%		1.99%
Average Receive Rate	0.45%		0.45%		0.55%
Net Estimated Fair Value	$ (158)		$ (158)		$ (18)
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate	0.45%		0.45%		0.55%
Derivative, Average Remaining Maturity			9 years 4 months 24 days		8 years 2 months 12 days
Not Designated as Hedging Instrument [Member]
Notional Amount of Interest Rate Derivatives	$ 48,850		$ 48,850		$ 30,250
Notional Amount	$ 48,850		$ 48,850		$ 30,250
Average Fixed Pay Rate	1.43%		1.43%		1.57%
Average Receive Rate	0.35%		0.35%		0.35%
Net Estimated Fair Value	$ (1,436)		$ (1,436)		$ (782)
Interest Rate Derivative Not Designated As Hedging Instruments Average receive Rate	0.35%		0.35%		0.35%
Derivative, Average Remaining Maturity			4 years 3 months 18 days		3 years 6 months

Derivative and Other Hedging Instruments (Summary Of Outstanding Interest Rate Swaps Agreements Designated As Hedges in the Future) (Details) - Payer Swaption [Member] $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2011 USD ($)	Sep. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)
Cost		$ 152	$ 49
Fair Value	$ 11	$ 57	11
Average Months to Expiration	7	19
Notional Amount	$ 3,200	$ 8,550	$ 3,200
Pay Rate	3.41%	3.30%
Receive Rate		1M / 3M LIBOR	1M / 3M LIBOR
Term (Years)		7 years 8 months 12 days	7 years 8 months 12 days

Derivative and Other Hedging Instruments (Summary of Outstanding Total Return Swaps) (Details) - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Notional Amount	$ 3,774	$ (103)
Fair Value of Derivative Instruments	$ 109	$ 13

Derivative and Other Hedging Instruments (Summary Of Derivatives Outstanding Not Designated As Hedging Instruments) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Gain On Interest Only Securities Remeasured at Fair Value Through Earnings					$ 19
Gain Loss on Other Debt	$ 24				32
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	0				0
Notional Amount	3,774				3,774		$ (103)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	51	$ 52	$ 52	$ (512)	$ 155	$ (704)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net				(71)		(140)
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net				1		(2)
Derivative, Higher Remaining Maturity Range					6 months		5 months
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(456)			(198)	$ (1,428)	(317)
Loss on interest only securities remeasured at fair value through earnings	20			(28)		(24)
Derivative assets, at fair value [Member]
Derivative assets not designated as hedging instruments	292				292		$ 82
Derivative liabilities, at fair value [Member]
Derivative liabilities not designated as hedging instruments	(1,562)				(1,562)		(853)
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	18,169	7,447		5,436	18,169	5,436	3,699	$ 3,432	$ 512
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(26,234)			(17,877)	(76,028)	(37,298)
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net						(3)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	36,956			19,881	90,498	42,222
Additions Due to Hedge De-Designations				0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	222			73	343	119
Purchases Of TBAs And Forward Settling Agency Securities [Member] \| Derivative assets, at fair value [Member]
Derivative assets not designated as hedging instruments	186				186		54
Purchases Of TBAs And Forward Settling Agency Securities [Member] \| Derivative liabilities, at fair value [Member]
Derivative assets not designated as hedging instruments	(20)				(20)		0
Sale Of TBA And Forward Settling Agency Securities [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	14,395	10,851		6,254	14,395	6,254	3,803	4,282	1,361
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(49,774)			(35,895)	(120,438)	(83,902)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	53,318			37,867	131,030	88,795
Additions Due to Hedge De-Designations				0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(173)			(146)	(402)	(291)
Sale Of TBA And Forward Settling Agency Securities [Member] \| Derivative assets, at fair value [Member]
Derivative assets not designated as hedging instruments	43				43		3
Sale Of TBA And Forward Settling Agency Securities [Member] \| Derivative liabilities, at fair value [Member]
Derivative liabilities not designated as hedging instruments	(100)				(100)		(44)
Sale Of TBA And Forward Settling Agency Securities [Member]
Unrealized Gain On Derivative Instrument And Trading Securities					1
Gain on Derivative Instruments and Trading Securities				5		33
Interest Rate Swaps [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	48,850	48,550		26,950	48,850	26,950	30,250	150	50
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(3,150)			0	(4,700)	100
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	3,450			2,900	23,300	2,900
Additions Due to Hedge De-Designations				23,900		23,900
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(438)			(3)	(1,067)	(8)
Interest Rate Swaps [Member] \| Derivative assets, at fair value [Member]
Derivative assets not designated as hedging instruments							13
Interest Rate Swaps [Member] \| Derivative liabilities, at fair value [Member]
Derivative liabilities not designated as hedging instruments	(1,442)				(1,442)		(795)
Treasury Futures [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	0	1,919		350	0	350	783		0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(1,919)				(4,621)	(50)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	0				3,838	400
Additions Due to Hedge De-Designations						0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(27)				(91)	2
Treasury Futures [Member] \| Derivative liabilities, at fair value [Member]
Derivative assets not designated as hedging instruments	0				0		(14)
Markit IOS Total Return Swaps - Short [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	0	181		323	0	323	206	309	0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(181)			(309)	(206)	(313)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	0			323	0	636
Additions Due to Hedge De-Designations				0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0			20	0	17
Payer Swaption [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	8,550	8,800		3,250	8,550	3,250	3,200	4,050	850
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(2,250)			(1,050)	(6,800)	(2,050)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	2,000			250	12,150	4,450
Additions Due to Hedge De-Designations				0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(25)			(33)	(96)	(58)
Payer Swaption [Member] \| Derivative assets, at fair value [Member]
Derivative assets not designated as hedging instruments	57				57		11
Short Sales Of U S Government Securities [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments	7,295	1,250		465	7,295	465	880	1,464	250
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(5,505)			(4,449)	(24,065)	(11,759)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	11,550			3,450	30,480	11,974
Additions Due to Hedge De-Designations				0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(15)			(92)	(115)	(92)
Markit IOS Total Return Swaps - Long [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments		37		65		65	41	683	0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period	(37)			(683)	(41)	(1,089)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period	0			65	0	1,154
Additions Due to Hedge De-Designations				0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	0			(19)	0	(6)
Markit IOS Total Return Swaps - Long [Member] \| Derivative assets, at fair value [Member]
Derivative assets not designated as hedging instruments	0				$ 0		$ 1
Receiver Swaption [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments				0		0			0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period						(250)
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period						250
Additions Due to Hedge De-Designations						0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net						(1)
Not Designated as Hedging Instrument [Member]
Derivative, Average Remaining Maturity					4 years 3 months 18 days		3 years 6 months
Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member]
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge	(536)				$ (536)
Deferred gain loss discontinued interest rate swap expected to be reclassified from OCI to interest expense next twelve months					$ 194
Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member] \| Interest Rate Swaps [Member]
Derivative, Average Remaining Maturity					2 years 6 months 10 days
Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member] \| Interest Rate Swap [Member]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	51	$ 52	$ 52
Put Option [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments				0		0		$ 0	$ 0
Notional Amount Of Derivatives Not Designated As Hedging Instruments Settlement Expiration During The Period				0		200
Notional Amount Of Derivatives Not Designated As Hedging Instruments Additions During The Period				350		(200)
Additions Due to Hedge De-Designations				0		0
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net				2		1
U.S. Treasury futures [Member]
Notional Amount of Other Derivatives Not Designated as Hedging Instruments				$ 350		$ 350
Interest Rate Swap [Member]
Notional Amount	$ 3,100				$ 3,100		$ 2,600

Derivative and Other Hedging Instruments (Effect Of Derivative Instruments Not Designated As Hedges On Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Unrealized Gain On Derivative Instrument And Trading Securities	$ 20	$ 28	$ 19	$ 24
Notional Amount	0		0
Amount Gain/(Loss) Recognized in Income on Derivatives	(456)	(198)	(1,428)	(317)
Put Option [Member]
Notional Amount		0		0
Additions		350		(200)
Additions Due to Hedge De-Designations		0		0
Settlement, Expirations or Exercise		0		200
Notional Amount		0		0
Amount Gain/(Loss) Recognized in Income on Derivatives		2		1
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Notional Amount	7,447	3,432	3,699	512
Additions	36,956	19,881	90,498	42,222
Additions Due to Hedge De-Designations		0		0
Settlement, Expirations or Exercise	(26,234)	(17,877)	(76,028)	(37,298)
Notional Amount	18,169	5,436	18,169	5,436
Amount Gain/(Loss) Recognized in Income on Derivatives	222	73	343	119
Sale Of TBA And Forward Settling Agency Securities [Member]
Notional Amount	10,851	4,282	3,803	1,361
Additions	53,318	37,867	131,030	88,795
Additions Due to Hedge De-Designations		0		0
Settlement, Expirations or Exercise	(49,774)	(35,895)	(120,438)	(83,902)
Notional Amount	14,395	6,254	14,395	6,254
Amount Gain/(Loss) Recognized in Income on Derivatives	(173)	(146)	(402)	(291)
Payer Interest Rate Swaps [Member]
Notional Amount	48,550	150	30,250	50
Additions	3,450	2,900	23,300	2,900
Additions Due to Hedge De-Designations		23,900		23,900
Settlement, Expirations or Exercise	(3,150)	0	(4,700)	100
Notional Amount	48,850	26,950	48,850	26,950
Amount Gain/(Loss) Recognized in Income on Derivatives	(438)	(3)	(1,067)	(8)
Payer Swaption [Member]
Notional Amount	8,800	4,050	3,200	850
Additions	2,000	250	12,150	4,450
Additions Due to Hedge De-Designations		0		0
Settlement, Expirations or Exercise	(2,250)	(1,050)	(6,800)	(2,050)
Notional Amount	8,550	3,250	8,550	3,250
Amount Gain/(Loss) Recognized in Income on Derivatives	(25)	(33)	(96)	(58)
Receiver Swaption [Member]
Notional Amount				0
Additions				250
Additions Due to Hedge De-Designations				0
Settlement, Expirations or Exercise				(250)
Notional Amount		0		0
Amount Gain/(Loss) Recognized in Income on Derivatives				(1)
Short Sales Of U S Government Securities [Member]
Notional Amount	1,250	1,464	880	250
Additions	11,550	3,450	30,480	11,974
Additions Due to Hedge De-Designations		0		0
Settlement, Expirations or Exercise	(5,505)	(4,449)	(24,065)	(11,759)
Notional Amount	7,295	465	7,295	465
Amount Gain/(Loss) Recognized in Income on Derivatives	(15)	(92)	(115)	(92)
Treasury Futures [Member]
Notional Amount	1,919		783	0
Additions	0		3,838	400
Additions Due to Hedge De-Designations				0
Settlement, Expirations or Exercise	(1,919)		(4,621)	(50)
Notional Amount	0	350	0	350
Amount Gain/(Loss) Recognized in Income on Derivatives	(27)		(91)	2
Markit IOS Total Return Swaps - Long [Member]
Notional Amount	37	683	41	0
Additions	0	65	0	1,154
Additions Due to Hedge De-Designations		0		0
Settlement, Expirations or Exercise	(37)	(683)	(41)	(1,089)
Notional Amount		65		65
Amount Gain/(Loss) Recognized in Income on Derivatives	0	(19)	0	(6)
Markit IOS Total Return Swaps - Short [Member]
Notional Amount	181	309	206	0
Additions	0	323	0	636
Additions Due to Hedge De-Designations		0		0
Settlement, Expirations or Exercise	(181)	(309)	(206)	(313)
Notional Amount	0	323	0	323
Amount Gain/(Loss) Recognized in Income on Derivatives	$ 0	$ 20	$ 0	$ 17

Fair Value Measurements (Details) - USD ($) $ in Thousands	9 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	$ 968,000
Financial Instruments, Owned, Mortgages, Mortgage-backed and Asset-backed Securities, at Fair Value	88,020,000	$ 54,625,000
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value	0	101,000
Derivative Assets	292,000	82,000
Obligation to return securities borrowed under reverse repurchase agreements, at fair value	(7,265,000)	(899,000)
Derivative Liabilities	$ (1,562,000)	(853,000)
Transfers between hierarchy levels	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	$ 968,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, Mortgages, Mortgage-backed and Asset-backed Securities, at Fair Value	0	0
Assets, Fair Value Disclosure	0	101,000
Liabilities, Fair Value Disclosure	7,265,000	913,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	0	(14,000)
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other derivative instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value		101,000
Derivative Assets	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Other derivative instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	89,932,000	54,765,000
Obligation to return securities borrowed under reverse repurchase agreements, at fair value	0	0
Liabilities, Fair Value Disclosure	2,530,000	839,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other derivative instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities		(44,000)
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	1,442,000	13,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Other derivative instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	286,000	69,000
Derivative Liabilities	(120,000)
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, Mortgages, Mortgage-backed and Asset-backed Securities, at Fair Value	0	0
Assets, Fair Value Disclosure	0	0
Obligation to return securities borrowed under reverse repurchase agreements, at fair value	0	0
Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other derivative instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Other derivative instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	0	0
Derivative assets, at fair value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	292,000	82,000
Derivative liabilities, at fair value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(1,562,000)	(853,000)
Interest Rate Swaps [Member] \| Derivative assets, at fair value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		13,000
Interest Rate Swaps [Member] \| Derivative assets, at fair value [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	6,000
Interest Rate Swaps [Member] \| Derivative liabilities, at fair value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	(1,442,000)	(795,000)
Treasury Futures [Member] \| Derivative liabilities, at fair value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	0	(14,000)
Collateralized Mortgage Backed Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, Mortgages, Mortgage-backed and Asset-backed Securities, at Fair Value	$ 89,640,000	54,683,000
Interest Rate Swap [Member] \| Interest Rate Swaps [Member] \| Derivative liabilities, at fair value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value		$ 795,000

Stockholders' Equity (Summary of Follow-on Public Offerings of Common Stock) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Billions	1 Months Ended		3 Months Ended
	Jul. 31, 2012	Mar. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012
Preferred Stock, Shares Authorized			3.1
Public offering price per share		$ 29.00	$ 33.70		$ 29.00
Public offering of common stock	36.8	71.2
Public offering net proceeds	$ 1.2	$ 2.1
Common Stock [Member]
Public offering of common stock			36.8	4.8	75.9

Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended			3 Months Ended			9 Months Ended
	Jul. 31, 2012	Apr. 30, 2012	Mar. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Preferred stock, shares issued				6.9			6.9		0.0
Issuance of common stock, value				$ 1,240	$ 155	$ 2,205
Public offering of common stock	36.8		71.2
Preferred Stock, Par or Stated Value Per Share				$ 0.01			$ 0.01		$ 0.01
Proceeds from Issuance of Preferred Stock and Preference Stock					$ 167		$ 167
At-the-Market Offering Program [Member]
Public offering, average price per share							$ 31.41
Issuance of common stock, value							$ 298
Public offering of common stock							9.5
Shares available for issuance				16.7			16.7
Dividend Reinvestment And Direct Stock Purchase Plan [Member]
Shares available for issuance				4.7			4.7
Issuance of Equity [Member]
Preferred stock, shares issued		6.9
Preferred Stock, Par or Stated Value Per Share		$ 24.21
Proceeds from Issuance of Preferred Stock and Preference Stock		$ 167
Preferred Stock, Dividend Rate, Percentage		8.00%
Preferred Stock, Liquidation Preference Per Share		$ 25.00

Subsequent Event (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended				3 Months Ended			9 Months Ended
	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Mar. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Subsequent Event [Line Items]
Stock Repurchase Program, Authorized Amount	$ 500
Issuance of common stock, shares		36.8		71.2
Preferred stock, shares issued					6.9			6.9		0.0
Dividends declared per common share					$ 1.25		$ 1.40	$ 3.75	$ 4.20
Preferred Stock, Par or Stated Value Per Share					0.01			$ 0.01		$ 0.01
Proceeds from Issuance of Preferred Stock and Preference Stock						$ 167		$ 167
Sale of Stock, Price Per Share				$ 29.00	$ 33.70			$ 33.70
Proceed From Issuance of Common Stock, Net of Issuance Costs		$ 1,200		$ 2,100
Issuance of Equity [Member]
Subsequent Event [Line Items]
Preferred stock, shares issued			6.9
Preferred Stock, Par or Stated Value Per Share			$ 24.21
Proceeds from Issuance of Preferred Stock and Preference Stock			$ 167
Preferred Stock, Dividend Rate, Percentage			8.00%
Preferred Stock, Liquidation Preference Per Share			$ 25.00