Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jan. 01, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 31,150	$ 39,067	$ 35,541	$ 43,846
Provision (benefit) for loan losses	(1,394)	(1,051)	(357)	(3,481)
Charge-offs	(777)	(1,561)	(8,213)	(5,071)
Recoveries	168	275	1,051	1,124
Transfers	0	0	0	0
Other	(12)	201	1,113	513
Ending balance	29,135	36,931	29,135	36,931
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	29,724	36,643	33,117	40,521
Provision (benefit) for loan losses	(1,732)	(1,439)	(290)	(3,629)
Charge-offs	(753)	(1,453)	(8,147)	(4,820)
Recoveries	165	271	1,036	902
Transfers	263	368	878	1,127
Other	(12)	172	1,061	461
Ending balance	27,655	34,562	27,655	34,562
Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,426	2,424	2,424	3,325
Provision (benefit) for loan losses	338	388	(67)	148
Charge-offs	(24)	(108)	(66)	(251)
Recoveries	3	4	15	222
Transfers	(263)	(368)	(878)	(1,127)
Other	0	29	52	52
Ending balance	1,480	2,369	1,480	2,369
Single-family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	30,876	38,643	35,177	43,307
Provision (benefit) for loan losses	(1,392)	(999)	(293)	(3,371)
Charge-offs	(770)	(1,547)	(8,172)	(4,998)
Recoveries	164	275	1,047	1,124
Transfers	0	0	0	0
Other	(13)	198	1,106	508
Ending balance	28,865	36,570	28,865	36,570
Single-family [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	29,624	36,400	32,956	40,202
Provision (benefit) for loan losses	(1,722)	(1,393)	(249)	(3,563)
Charge-offs	(748)	(1,439)	(8,108)	(4,747)
Recoveries	161	271	1,032	902
Transfers	262	366	877	1,123
Other	(13)	170	1,056	458
Ending balance	27,564	34,375	27,564	34,375
Single-family [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,252	2,243	2,221	3,105
Provision (benefit) for loan losses	330	394	(44)	192
Charge-offs	(22)	(108)	(64)	(251)
Recoveries	3	4	15	222
Transfers	(262)	(366)	(877)	(1,123)
Other	0	28	50	50
Ending balance	1,301	2,195	1,301	2,195
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	274	424	364	539
Provision (benefit) for loan losses	(2)	(52)	(64)	(110)
Charge-offs	(7)	(14)	(41)	(73)
Recoveries	4	0	4	0
Transfers	0	0	0	0
Other	1	3	7	5
Ending balance	270	361	270	361
Multifamily [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	100	243	161	319
Provision (benefit) for loan losses	(10)	(46)	(41)	(66)
Charge-offs	(5)	(14)	(39)	(73)
Recoveries	4	0	4	0
Transfers	1	2	1	4
Other	1	2	5	3
Ending balance	91	187	91	187
Multifamily [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	174	181	203	220
Provision (benefit) for loan losses	8	(6)	(23)	(44)
Charge-offs	(2)	0	(2)	0
Recoveries	0	0	0	0
Transfers	(1)	(2)	(1)	(4)
Other	0	1	2	2
Ending balance	$ 179	$ 174	$ 179	$ 174