Allowance for Loan Losses Allowance Rollforward (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	$ (1,558)	[1]	$ (5,449)	[1]	$ (2,430)	[1]	$ (6,433)	[1]
Charge-offs	(1,911)	[2],[3]	(2,218)	[2],[3]	(3,510)	[2],[3]	(4,938)	[2],[3]
Recoveries	458		572		849		1,844
Transfers	0	[4]	0	[4]	0	[4]	0	[4]
Other	167	[5]	277	[5]	312	[5]	375	[5]
Ending balance	39,067		49,643		39,067		49,643		41,911	43,846	56,461	58,795
Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(1,296)	[1]	(4,134)	[1]	(2,190)	[1]	(4,661)	[1]
Charge-offs	(1,869)	[2],[3]	(2,081)	[2],[3]	(3,367)	[2],[3]	(4,752)	[2],[3]
Recoveries	311		466		631		1,493
Transfers	339	[4]	776	[4]	759	[4]	1,908	[4]
Other	154	[5]	245	[5]	289	[5]	318	[5]
Ending balance	36,643		44,825		36,643		44,825		39,004	40,521	49,553	50,519
Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(262)	[1]	(1,315)	[1]	(240)	[1]	(1,772)	[1]
Charge-offs	(42)	[2],[3]	(137)	[2],[3]	(143)	[2],[3]	(186)	[2],[3]
Recoveries	147		106		218		351
Transfers	(339)	[4]	(776)	[4]	(759)	[4]	(1,908)	[4]
Other	13	[5]	32	[5]	23	[5]	57	[5]
Ending balance	2,424		4,818		2,424		4,818		2,907	3,325	6,908	8,276
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(1,528)	[1]	(5,428)	[1]	(2,372)	[1]	(6,267)	[1]
Charge-offs	(1,903)	[3]	(2,152)	[3]	(3,451)	[3]	(4,871)	[3]
Recoveries	458		572		849		1,844
Transfers	0	[4]	0	[4]	0	[4]	0	[4]
Other	168	[5]	277	[5]	310	[5]	377	[5]
Ending balance	38,643		48,770		38,643		48,770		41,448	43,307	55,501	57,687
Single-Family [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(1,288)	[1]	(4,098)	[1]	(2,170)	[1]	(4,534)	[1]
Charge-offs	(1,861)	[3]	(2,015)	[3]	(3,308)	[3]	(4,685)	[3]
Recoveries	311		466		631		1,493
Transfers	337	[4]	768	[4]	757	[4]	1,891	[4]
Other	155	[5]	244	[5]	288	[5]	319	[5]
Ending balance	36,400		44,332		36,400		44,332		38,746	40,202	48,967	49,848
Single-Family [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(240)	[1]	(1,330)	[1]	(202)	[1]	(1,733)	[1]
Charge-offs	(42)	[3]	(137)	[3]	(143)	[3]	(186)	[3]
Recoveries	147		106		218		351
Transfers	(337)	[4]	(768)	[4]	(757)	[4]	(1,891)	[4]
Other	13	[5]	33	[5]	22	[5]	58	[5]
Ending balance	2,243		4,438		2,243		4,438		2,702	3,105	6,534	7,839
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(30)	[1]	(21)	[1]	(58)	[1]	(166)	[1]
Charge-offs	(8)	[3]	(66)	[3]	(59)	[3]	(67)	[3]
Transfers	0	[4]	0	[4]	0	[4]	0	[4]
Other	(1)	[5]	0	[5]	2	[5]	(2)	[5]
Ending balance	424		873		424		873		463	539	960	1,108
Multifamily [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(8)	[1]	(36)	[1]	(20)	[1]	(127)	[1]
Charge-offs	(8)	[3]	(66)	[3]	(59)	[3]	(67)	[3]
Transfers	2	[4]	8	[4]	2	[4]	17	[4]
Other	(1)	[5]	1	[5]	1	[5]	(1)	[5]
Ending balance	243		493		243		493		258	319	586	671
Multifamily [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
(Benefit) provision for loan losses	(22)	[1]	15	[1]	(38)	[1]	(39)	[1]
Charge-offs	0	[3]	0	[3]	0	[3]	0	[3]
Transfers	(2)	[4]	(8)	[4]	(2)	[4]	(17)	[4]
Other	0	[5]	(1)	[5]	1	[5]	(1)	[5]
Ending balance	181		380		181		380		205	220	374	437
Interest Receivable [Member]
Allowance for Loan Losses [Roll Forward]
Charge-offs	$ 75		$ 122		$ 169		$ 237

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

[2] Total charge-offs include accrued interest of $75 million and $122 million for the three months ended June 30, 2014 and 2013, respectively, and $169 million and $237 million for the six months ended June 30, 2014 and 2013, respectively.

[3] 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.

[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 loan losses, charge-offs, recoveries and transfer activity included in this table reflect 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.