Derivative Instruments Derivatives 1 - Notional and FV Position (Details) (USD $)	Jun. 30, 2013		Dec. 31, 2012
Asset Derivatives [Abstract]
Notional amount	$ 332,972,000,000		$ 396,866,000,000
Derivatives asset, estimated fair value	3,449,000,000		435,000,000
Netting adjustment	(12,073,000,000)	[1]	(15,791,000,000)	[1]
Derivative Liabilities [Abstract]
Notional amount	575,849,000,000		464,145,000,000
Derivative liability, estimated fair value	(2,904,000,000)		(705,000,000)
Table Footnote [Abstract]
Cash collateral posted for derivative instruments	4,400,000,000		6,300,000,000
Cash collateral received for derivative instruments	672,000,000		0
Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	244,016,000,000		331,075,000,000
Derivatives asset, estimated fair value	12,216,000,000		14,828,000,000
Accrued interest receivable, estimated fair value	1,116,000,000		1,242,000,000
Netting adjustment	(12,073,000,000)	[1],[2]	(15,791,000,000)	[1],[2]
Total net risk management derivatives	1,259,000,000		279,000,000
Derivative Liabilities [Abstract]
Notional amount	505,020,000,000		370,879,000,000
Derivative liability, estimated fair value	(15,750,000,000)		(20,946,000,000)
Accrued interest payable, estimated fair value	(1,268,000,000)		(1,508,000,000)
Netting adjustment	15,785,000,000	[1],[2]	22,046,000,000	[1],[2]
Total net risk management derivatives	(1,233,000,000)		(408,000,000)
Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	88,956,000,000		65,791,000,000
Derivatives asset, estimated fair value	2,190,000,000		156,000,000
Netting adjustment	0	[1]	0	[1]
Derivative Liabilities [Abstract]
Notional amount	70,829,000,000		93,266,000,000
Derivative liability, estimated fair value	(1,671,000,000)		(297,000,000)
Netting adjustment	0	[1]	0	[1]
Pay-fixed Swap [Member] | Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	87,427,000,000		19,450,000,000
Derivatives asset, estimated fair value	4,306,000,000		270,000,000
Derivative Liabilities [Abstract]
Notional amount	159,686,000,000		239,017,000,000
Derivative liability, estimated fair value	(9,109,000,000)		(18,237,000,000)
Receive-fixed Swap [Member] | Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	82,617,000,000		231,346,000,000
Derivatives asset, estimated fair value	5,907,000,000		10,514,000,000
Derivative Liabilities [Abstract]
Notional amount	213,892,000,000		57,190,000,000
Derivative liability, estimated fair value	(4,554,000,000)		(200,000,000)
Basis Swap [Member] | Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	19,700,000,000		23,199,000,000
Derivatives asset, estimated fair value	79,000,000		151,000,000
Derivative Liabilities [Abstract]
Notional amount	7,200,000,000		1,700,000,000
Derivative liability, estimated fair value	(1,000,000)		0
Foreign Currency Swap [Member] | Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	408,000,000		686,000,000
Derivatives asset, estimated fair value	111,000,000		193,000,000
Derivative Liabilities [Abstract]
Notional amount	580,000,000		509,000,000
Derivative liability, estimated fair value	(71,000,000)		(45,000,000)
Pay-fixed Swaption [Member] | Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	33,750,000,000		33,050,000,000
Derivatives asset, estimated fair value	335,000,000		102,000,000
Derivative Liabilities [Abstract]
Notional amount	62,325,000,000		36,225,000,000
Derivative liability, estimated fair value	(933,000,000)		(184,000,000)
Receive-fixed Swaption [Member] | Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	15,020,000,000		15,970,000,000
Derivatives asset, estimated fair value	1,451,000,000		3,572,000,000
Derivative Liabilities [Abstract]
Notional amount	61,325,000,000		36,225,000,000
Derivative liability, estimated fair value	(1,082,000,000)		(2,279,000,000)
Other [Member] | Risk Management Derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	5,094,000,000	[3]	7,374,000,000	[3]
Derivatives asset, estimated fair value	27,000,000	[3]	26,000,000	[3]
Derivative Liabilities [Abstract]
Notional amount	12,000,000	[3]	13,000,000	[3]
Derivative liability, estimated fair value	0	[3]	(1,000,000)	[3]
Mortgage Commitments to Purchase Whole Loans [Member] | Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	3,292,000,000		12,360,000,000
Derivatives asset, estimated fair value	23,000,000		27,000,000
Derivative Liabilities [Abstract]
Notional amount	9,719,000,000		5,232,000,000
Derivative liability, estimated fair value	(298,000,000)		(8,000,000)
Forward Contracts to Purchase Mortgage-related Securities [Member] | Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	13,779,000,000		34,545,000,000
Derivatives asset, estimated fair value	116,000,000		103,000,000
Derivative Liabilities [Abstract]
Notional amount	41,496,000,000		12,557,000,000
Derivative liability, estimated fair value	(1,212,000,000)		(23,000,000)
Forward Contracts to Sell Mortgage-related Securities [Member] | Mortgage commitment derivatives [Member]
Asset Derivatives [Abstract]
Notional amount	71,885,000,000		18,886,000,000
Derivatives asset, estimated fair value	2,051,000,000		26,000,000
Derivative Liabilities [Abstract]
Notional amount	19,614,000,000		75,477,000,000
Derivative liability, estimated fair value	$ (161,000,000)		$ (266,000,000)

[1] Represents the effect of the 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 and accrued interest.

[2] 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 $4.4 billion and $6.3 billion as of June 30, 2013 and December 31, 2012, respectively. Since the agreements related to clearing contracts through derivatives clearing organizations do not provide us with a legal right of offset, no netting adjustments have been made for those contracts. Cash collateral received was $672 million as of June 30, 2013. No cash collateral was received as of December 31, 2012.

[3] 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.