Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 27,951	$ 35,541
Provision (benefit) for loan losses	(1,032)	8
Charge-offs	(1,284)	(5,362)
Recoveries	120	622
Transfers	0	0
Other	64	1,011
Ending balance	25,819	31,820
Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	26,510	33,117
Provision (benefit) for loan losses	(1,129)	168
Charge-offs	(1,258)	(5,343)
Recoveries	118	614
Transfers	252	359
Other	64	958
Ending balance	24,557	29,873
Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,441	2,424
Provision (benefit) for loan losses	97	(160)
Charge-offs	(26)	(19)
Recoveries	2	8
Transfers	(252)	(359)
Other	0	53
Ending balance	1,262	1,947
Single-family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	27,709	35,177
Provision (benefit) for loan losses	(1,016)	58
Charge-offs	(1,279)	(5,347)
Recoveries	119	622
Transfers	0	0
Other	64	1,004
Ending balance	25,597	31,514
Single-family [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	26,439	32,956
Provision (benefit) for loan losses	(1,126)	205
Charge-offs	(1,253)	(5,328)
Recoveries	117	614
Transfers	249	359
Other	64	953
Ending balance	24,490	29,759
Single-family [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,270	2,221
Provision (benefit) for loan losses	110	(147)
Charge-offs	(26)	(19)
Recoveries	2	8
Transfers	(249)	(359)
Other	0	51
Ending balance	1,107	1,755
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	242	364
Provision (benefit) for loan losses	(16)	(50)
Charge-offs	(5)	(15)
Recoveries	1	0
Transfers	0	0
Other	0	7
Ending balance	222	306
Multifamily [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	71	161
Provision (benefit) for loan losses	(3)	(37)
Charge-offs	(5)	(15)
Recoveries	1	0
Transfers	3	0
Other	0	5
Ending balance	67	114
Multifamily [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	171	203
Provision (benefit) for loan losses	(13)	(13)
Charge-offs	0	0
Recoveries	0	0
Transfers	(3)	0
Other	0	2
Ending balance	$ 155	$ 192