Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 01, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 35,541	$ 43,846	$ 58,795
Provision (benefit) for loan losses	(158)	(3,885)	(9,316)
Charge-offs	(9,774)	(6,469)	(8,867)
Recoveries	1,140	1,440	2,626
Transfers	0	0	0
Other	1,202	609	608
Ending balance	27,951	35,541	43,846
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	33,117	40,521	50,519
Provision (benefit) for loan losses	(321)	(4,425)	(6,984)
Charge-offs	(9,687)	(6,244)	(8,611)
Recoveries	1,124	1,190	2,115
Transfers	1,127	1,517	2,962
Other	1,150	558	520
Ending balance	26,510	33,117	40,521
Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	2,424	3,325	8,276
Provision (benefit) for loan losses	163	540	(2,332)
Charge-offs	(87)	(225)	(256)
Recoveries	16	250	511
Transfers	(1,127)	(1,517)	(2,962)
Other	52	51	88
Ending balance	1,441	2,424	3,325
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	35,177	43,307	57,687
Provision (benefit) for loan losses	(68)	(3,781)	(8,896)
Charge-offs	(9,731)	(6,393)	(8,714)
Recoveries	1,136	1,440	2,626
Transfers	0	0	0
Other	1,195	604	604
Ending balance	27,709	35,177	43,307
Single-Family [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	32,956	40,202	49,848
Provision (benefit) for loan losses	(258)	(4,334)	(6,751)
Charge-offs	(9,647)	(6,168)	(8,458)
Recoveries	1,120	1,190	2,115
Transfers	1,123	1,513	2,932
Other	1,145	553	516
Ending balance	26,439	32,956	40,202
Single-Family [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	2,221	3,105	7,839
Provision (benefit) for loan losses	190	553	(2,145)
Charge-offs	(84)	(225)	(256)
Recoveries	16	250	511
Transfers	(1,123)	(1,513)	(2,932)
Other	50	51	88
Ending balance	1,270	2,221	3,105
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	364	539	1,108
Provision (benefit) for loan losses	(90)	(104)	(420)
Charge-offs	(43)	(76)	(153)
Recoveries	4	0	0
Transfers	0	0	0
Other	7	5	4
Ending balance	242	364	539
Multifamily [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	161	319	671
Provision (benefit) for loan losses	(63)	(91)	(233)
Charge-offs	(40)	(76)	(153)
Recoveries	4	0	0
Transfers	4	4	30
Other	5	5	4
Ending balance	71	161	319
Multifamily [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	203	220	437
Provision (benefit) for loan losses	(27)	(13)	(187)
Charge-offs	(3)	0	0
Recoveries	0	0	0
Transfers	(4)	(4)	(30)
Other	2	0	0
Ending balance	$ 171	$ 203	$ 220