Allowance for Loan Losses Allowance Rollforward (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Mar. 31, 2013 Single-Family [Member]		Mar. 31, 2012 Single-Family [Member]		Mar. 31, 2013 Multifamily [Member]		Mar. 31, 2012 Multifamily [Member]		Mar. 31, 2013 Fannie Mae [Member]		Mar. 31, 2012 Fannie Mae [Member]		Mar. 31, 2013 Fannie Mae [Member] Single-Family [Member]		Mar. 31, 2012 Fannie Mae [Member] Single-Family [Member]		Mar. 31, 2013 Fannie Mae [Member] Multifamily [Member]		Mar. 31, 2012 Fannie Mae [Member] Multifamily [Member]		Mar. 31, 2013 Consolidated Trusts [Member]		Mar. 31, 2012 Consolidated Trusts [Member]		Mar. 31, 2013 Consolidated Trusts [Member] Single-Family [Member]		Mar. 31, 2012 Consolidated Trusts [Member] Single-Family [Member]		Mar. 31, 2013 Consolidated Trusts [Member] Multifamily [Member]		Mar. 31, 2012 Consolidated Trusts [Member] Multifamily [Member]		Mar. 31, 2013 Interest Receivable [Member]	Mar. 31, 2012 Interest Receivable [Member]	Mar. 31, 2013 Interest Receivable [Member] Fannie Mae [Member]	Dec. 31, 2012 Interest Receivable [Member] Fannie Mae [Member]	Mar. 31, 2013 Interest Receivable [Member] Consolidated Trusts [Member]	Dec. 31, 2012 Interest Receivable [Member] Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 58,795		$ 72,156		$ 57,687		$ 70,633		$ 1,108		$ 1,523		$ 50,519		$ 57,309		$ 49,848		$ 56,294		$ 671		$ 1,015		$ 8,276		$ 14,847		$ 7,839		$ 14,339		$ 437		$ 508				$ 1,400	$ 1,500	$ 168	$ 192
(Benefit) provision for loan losses	(984)	[1]	1,980	[1]	(839)	[1]	2,020	[1]	(145)	[1]	(40)	[1]	(527)	[1]	1,383	[1]	(436)	[1]	1,400	[1]	(91)	[1]	(17)	[1]	(457)	[1]	597	[1]	(403)	[1]	620	[1]	(54)	[1]	(23)	[1]
Charge-offs	(2,720)	[2],[3]	(4,796)	[2],[3]	(2,719)	[2]	(4,667)	[2]	(1)	[2]	(129)	[2]	(2,671)	[2],[3]	(4,533)	[2],[3]	(2,670)	[2]	(4,404)	[2]	(1)	[2]	(129)	[2]	(49)	[2],[3]	(263)	[2],[3]	(49)	[2]	(263)	[2]	0	[2]	0	[2]	115	273
Recoveries	1,272		486		1,272		486						1,027		421		1,027		421						245		65		245		65
Transfers	0	[4]	0	[4]	0	[4]	0	[4]	0	[4]	0	[4]	1,132	[4]	2,201	[4]	1,123	[4]	2,193	[4]	9	[4]	8	[4]	(1,132)	[4]	(2,201)	[4]	(1,123)	[4]	(2,193)	[4]	(9)	[4]	(8)	[4]
Other	98	[5]	283	[5]	100	[5]	266	[5]	(2)	[5]	17	[5]	73	[5]	220	[5]	75	[5]	204	[5]	(2)	[5]	16	[5]	25	[5]	63	[5]	25	[5]	62	[5]	0	[5]	1	[5]
Ending balance	$ 56,461		$ 70,109		$ 55,501		$ 68,738		$ 960		$ 1,371		$ 49,553		$ 57,001		$ 48,967		$ 56,108		$ 586		$ 893		$ 6,908		$ 13,108		$ 6,534		$ 12,630		$ 374		$ 478				$ 1,400	$ 1,500	$ 168	$ 192

[1] (Benefit) provision for loan losses is included in benefit (provision) for credit losses in our condensed consolidated statements of operations and comprehensive income.

[2] While we purchase the substantial majority of loans that are four or more months delinquent from our MBS trusts, we do not exercise this option to purchase loans during a forbearance period. Charge-offs of consolidated trusts generally represent loans that remained in our consolidated trusts at the time of default.

[3] Total charge-offs include accrued interest of $115 million and $273 million for the three months ended March 31, 2013 and 2012, respectively.

[4] Includes transfers from trusts for delinquent loan purchases.

[5] Amounts represent the net activity recorded in our allowances for accrued interest receivable and preforeclosure property taxes and insurance receivable from borrowers. The (benefit) provision for credit losses, charge-offs, recoveries and transfer activity included in this table reflects all changes for both the allowance for loan losses and the valuation allowances for accrued interest and preforeclosure property taxes and insurance receivable that relate to the mortgage loans.