Allowance for Loan Losses Rollforward by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 27,951	$ 35,541	$ 43,846
Provision (benefit) for loan losses	(1,759)	(158)	(3,885)
Charge-offs	(3,266)	(9,774)	(6,469)
Recoveries	449	1,140	1,440
Transfers	0	0	0
Other	90	1,202	609
Ending balance	23,465	27,951	35,541
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	26,510	33,117	40,521
Provision (benefit) for loan losses	(1,741)	(321)	(4,425)
Charge-offs	(3,174)	(9,687)	(6,244)
Recoveries	419	1,124	1,190
Transfers	475	1,127	1,517
Other	90	1,150	558
Ending balance	22,579	26,510	33,117
Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,441	2,424	3,325
Provision (benefit) for loan losses	(18)	163	540
Charge-offs	(92)	(87)	(225)
Recoveries	30	16	250
Transfers	(475)	(1,127)	(1,517)
Other	0	52	51
Ending balance	886	1,441	2,424
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	27,709	35,177	43,307
Provision (benefit) for loan losses	(1,704)	(68)	(3,781)
Charge-offs	(3,254)	(9,731)	(6,393)
Recoveries	442	1,136	1,440
Transfers	0	0	0
Other	90	1,195	604
Ending balance	23,283	27,709	35,177
Single-Family [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	26,439	32,956	40,202
Provision (benefit) for loan losses	(1,692)	(258)	(4,334)
Charge-offs	(3,163)	(9,647)	(6,168)
Recoveries	412	1,120	1,190
Transfers	470	1,123	1,513
Other	90	1,145	553
Ending balance	22,556	26,439	32,956
Single-Family [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	1,270	2,221	3,105
Provision (benefit) for loan losses	(12)	190	553
Charge-offs	(91)	(84)	(225)
Recoveries	30	16	250
Transfers	(470)	(1,123)	(1,513)
Other	0	50	51
Ending balance	727	1,270	2,221
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	242	364	539
Provision (benefit) for loan losses	(55)	(90)	(104)
Charge-offs	(12)	(43)	(76)
Recoveries	7	4	0
Transfers	0	0	0
Other	0	7	5
Ending balance	182	242	364
Multifamily [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	71	161	319
Provision (benefit) for loan losses	(49)	(63)	(91)
Charge-offs	(11)	(40)	(76)
Recoveries	7	4	0
Transfers	5	4	4
Other	0	5	5
Ending balance	23	71	161
Multifamily [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	171	203	220
Provision (benefit) for loan losses	(6)	(27)	(13)
Charge-offs	(1)	(3)	0
Recoveries	0	0	0
Transfers	(5)	(4)	(4)
Other	0	2	0
Ending balance	$ 159	$ 171	$ 203