Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jan. 01, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 31,820	$ 41,911	$ 35,541	$ 43,846
Provision (benefit) for loan losses	1,029	(1,558)	1,037	(2,430)
Charge-offs	(2,074)	(1,911)	(7,436)	(3,510)
Recoveries	261	458	883	849
Transfers	0	0	0	0
Other	114	167	1,125	312
Ending balance	31,150	39,067	31,150	39,067
Nonaccrual Policy [Member]
Table Footnote [Abstract]
Allowance for accrued interest receivables, charge-offs					$ 1,100
Change in Accounting Method Accounted for as Change in Estimate [Member]
Table Footnote [Abstract]
Advisory Bulletin impact for HFI loans					1,800
Advisory Bulletin impact for preforeclosure property taxes and insurance receivable					$ 724
Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	29,873	39,004	33,117	40,521
Provision (benefit) for loan losses	1,274	(1,296)	1,442	(2,190)
Charge-offs	(2,051)	(1,869)	(7,394)	(3,367)
Recoveries	257	311	871	631
Transfers	256	339	615	759
Other	115	154	1,073	289
Ending balance	29,724	36,643	29,724	36,643
Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,947	2,907	2,424	3,325
Provision (benefit) for loan losses	(245)	(262)	(405)	(240)
Charge-offs	(23)	(42)	(42)	(143)
Recoveries	4	147	12	218
Transfers	(256)	(339)	(615)	(759)
Other	(1)	13	52	23
Ending balance	1,426	2,424	1,426	2,424
Single-family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	31,514	41,448	35,177	43,307
Provision (benefit) for loan losses	1,041	(1,528)	1,099	(2,372)
Charge-offs	(2,055)	(1,903)	(7,402)	(3,451)
Recoveries	261	458	883	849
Transfers	0	0	0	0
Other	115	168	1,119	310
Ending balance	30,876	38,643	30,876	38,643
Single-family [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	29,759	38,746	32,956	40,202
Provision (benefit) for loan losses	1,268	(1,288)	1,473	(2,170)
Charge-offs	(2,032)	(1,861)	(7,360)	(3,308)
Recoveries	257	311	871	631
Transfers	256	337	615	757
Other	116	155	1,069	288
Ending balance	29,624	36,400	29,624	36,400
Single-family [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,755	2,702	2,221	3,105
Provision (benefit) for loan losses	(227)	(240)	(374)	(202)
Charge-offs	(23)	(42)	(42)	(143)
Recoveries	4	147	12	218
Transfers	(256)	(337)	(615)	(757)
Other	(1)	13	50	22
Ending balance	1,252	2,243	1,252	2,243
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	306	463	364	539
Provision (benefit) for loan losses	(12)	(30)	(62)	(58)
Charge-offs	(19)	(8)	(34)	(59)
Transfers	0	0	0	0
Other	(1)	(1)	6	2
Ending balance	274	424	274	424
Multifamily [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	114	258	161	319
Provision (benefit) for loan losses	6	(8)	(31)	(20)
Charge-offs	(19)	(8)	(34)	(59)
Transfers	0	2	0	2
Other	(1)	(1)	4	1
Ending balance	100	243	100	243
Multifamily [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	192	205	203	220
Provision (benefit) for loan losses	(18)	(22)	(31)	(38)
Charge-offs	0	0	0	0
Transfers	0	(2)	0	(2)
Other	0	0	2	1
Ending balance	$ 174	$ 181	$ 174	$ 181