Derivative Instruments Notional and FV Position (Details) (USD $)	Jun. 30, 2012		Dec. 31, 2011
Asset Derivatives [Abstract]
Notional Amount	$ 406,005,000,000		$ 336,877,000,000
Estimated Fair Value	602,000,000		561,000,000
Derivative Liabilities [Abstract]
Notional Amount	385,588,000,000		377,748,000,000
Estimated Fair Value	(919,000,000)		(916,000,000)
Table Footnote [Abstract]
Cash collateral posted	7,200,000,000		6,800,000,000
Cash collateral received	3,000,000		779,000,000
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional Amount	335,790,000,000		293,090,000,000
Estimated Fair Value	15,499,000,000		15,085,000,000
Accrued interest receivable	1,087,000,000		920,000,000
Netting adjustment	(16,352,000,000)	[1]	(15,829,000,000)	[1]
Total net risk management derivatives	234,000,000		176,000,000
Derivative Liabilities [Abstract]
Notional Amount	279,584,000,000		320,100,000,000
Estimated Fair Value	(22,331,000,000)		(21,022,000,000)
Accrued interest payable	(1,482,000,000)		(1,238,000,000)
Netting adjustment	23,525,000,000	[1]	21,898,000,000	[1]
Total net risk management derivatives	(288,000,000)		(362,000,000)
Risk Management Derivatives [Member] | Pay-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional Amount	21,900,000,000		30,950,000,000
Estimated Fair Value	37,000,000		102,000,000
Derivative Liabilities [Abstract]
Notional Amount	207,327,000,000		155,807,000,000
Estimated Fair Value	(19,559,000,000)		(17,391,000,000)
Risk Management Derivatives [Member] | Receive-fixed Swap [Member]
Asset Derivatives [Abstract]
Notional Amount	241,703,000,000		170,668,000,000
Estimated Fair Value	9,791,000,000		8,118,000,000
Derivative Liabilities [Abstract]
Notional Amount	23,890,000,000		59,027,000,000
Estimated Fair Value	(14,000,000)		(93,000,000)
Risk Management Derivatives [Member] | Basis Swap [Member]
Asset Derivatives [Abstract]
Notional Amount	4,872,000,000		382,000,000
Estimated Fair Value	133,000,000		122,000,000
Derivative Liabilities [Abstract]
Notional Amount	16,050,000,000		9,240,000,000
Estimated Fair Value	(8,000,000)		(44,000,000)
Risk Management Derivatives [Member] | Foreign Currency Swap [Member]
Asset Derivatives [Abstract]
Notional Amount	621,000,000		581,000,000
Estimated Fair Value	160,000,000		155,000,000
Derivative Liabilities [Abstract]
Notional Amount	530,000,000		451,000,000
Estimated Fair Value	(64,000,000)		(62,000,000)
Risk Management Derivatives [Member] | Pay-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional Amount	34,400,000,000		48,600,000,000
Estimated Fair Value	109,000,000		165,000,000
Derivative Liabilities [Abstract]
Notional Amount	15,875,000,000		47,750,000,000
Estimated Fair Value	(81,000,000)		(194,000,000)
Risk Management Derivatives [Member] | Receive-fixed Swaption [Member]
Asset Derivatives [Abstract]
Notional Amount	23,895,000,000		33,695,000,000
Estimated Fair Value	5,214,000,000		6,371,000,000
Derivative Liabilities [Abstract]
Notional Amount	15,875,000,000		47,750,000,000
Estimated Fair Value	(2,605,000,000)		(3,238,000,000)
Risk Management Derivatives [Member] | Other [Member]
Asset Derivatives [Abstract]
Notional Amount	8,399,000,000	[2]	8,214,000,000	[2]
Estimated Fair Value	55,000,000	[2]	52,000,000	[2]
Derivative Liabilities [Abstract]
Notional Amount	37,000,000	[2]	75,000,000	[2]
Estimated Fair Value	0	[2]	0	[2]
Mortgage Commitment Derivatives [Member]
Asset Derivatives [Abstract]
Notional Amount	70,215,000,000		43,787,000,000
Estimated Fair Value	368,000,000		385,000,000
Derivative Liabilities [Abstract]
Notional Amount	106,004,000,000		57,648,000,000
Estimated Fair Value	(631,000,000)		(554,000,000)
Mortgage Commitment Derivatives [Member] | Mortgage Commitments to Purchase Whole Loans [Member]
Asset Derivatives [Abstract]
Notional Amount	11,825,000,000		9,710,000,000
Estimated Fair Value	63,000,000		73,000,000
Derivative Liabilities [Abstract]
Notional Amount	4,360,000,000		422,000,000
Estimated Fair Value	(5,000,000)		0
Mortgage Commitment Derivatives [Member] | Forward Contracts to Purchase Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional Amount	43,987,000,000		32,707,000,000
Estimated Fair Value	281,000,000		309,000,000
Derivative Liabilities [Abstract]
Notional Amount	18,566,000,000		2,570,000,000
Estimated Fair Value	(34,000,000)		(6,000,000)
Mortgage Commitment Derivatives [Member] | Forward Contracts to Sell Mortgage-related Securities [Member]
Asset Derivatives [Abstract]
Notional Amount	14,403,000,000		1,370,000,000
Estimated Fair Value	24,000,000		3,000,000
Derivative Liabilities [Abstract]
Notional Amount	83,078,000,000		54,656,000,000
Estimated Fair Value	$ (592,000,000)		$ (548,000,000)

[1] The netting adjustment represents the effect of the legal right to offset under legally enforceable master netting agreements to settle with the same counterparty on a net basis, including cash collateral posted and received. Cash collateral posted was $7.2 billion and $6.8 billion as of June 30, 2012 and December 31, 2011, respectively. Cash collateral received was $3 million and $779 million as of June 30, 2012 and December 31, 2011, respectively.

[2] Includes interest rate caps, futures, swap credit enhancements and mortgage insurance contracts that we account for as derivatives. The mortgage insurance contracts have payment provisions that are not based on a notional amount.