Allowance for Loan Losses Rollforward by Segment (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Jan. 01, 2015
Allowance for Loan Losses [Roll Forward]
Beginning balance	$ 35,541,000,000	$ 43,846,000,000
Provision (benefit) for loan losses	8,000,000	(872,000,000)
Charge-offs	(5,362,000,000)	(1,599,000,000)
Recoveries	622,000,000	391,000,000
Transfers	0	0
Other	1,011,000,000	145,000,000
Ending balance	31,820,000,000	41,911,000,000
Table Footnote [Abstract]
Advisory Bulletin Impact for Loans Held for Investment			1,800,000,000
Advisory Bulletin Impact for Taxes and Insurance Receivables			724,000,000
Nonaccrual Policy [Member]
Table Footnote [Abstract]
Allowance for Accrued Interest Receivables, Write Offs			1,100,000,000
Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	33,117,000,000	40,521,000,000
Provision (benefit) for loan losses	168,000,000	(894,000,000)
Charge-offs	(5,343,000,000)	(1,498,000,000)
Recoveries	614,000,000	320,000,000
Transfers	359,000,000	420,000,000
Other	958,000,000	135,000,000
Ending balance	29,873,000,000	39,004,000,000
Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	2,424,000,000	3,325,000,000
Provision (benefit) for loan losses	(160,000,000)	22,000,000
Charge-offs	(19,000,000)	(101,000,000)
Recoveries	8,000,000	71,000,000
Transfers	(359,000,000)	(420,000,000)
Other	53,000,000	10,000,000
Ending balance	1,947,000,000	2,907,000,000
Single-Family [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	35,177,000,000	43,307,000,000
Provision (benefit) for loan losses	58,000,000	(844,000,000)
Charge-offs	(5,347,000,000)	(1,548,000,000)
Recoveries	622,000,000	391,000,000
Transfers	0	0
Other	1,004,000,000	142,000,000
Ending balance	31,514,000,000	41,448,000,000
Single-Family [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	32,956,000,000	40,202,000,000
Provision (benefit) for loan losses	205,000,000	(882,000,000)
Charge-offs	(5,328,000,000)	(1,447,000,000)
Recoveries	614,000,000	320,000,000
Transfers	359,000,000	420,000,000
Other	953,000,000	133,000,000
Ending balance	29,759,000,000	38,746,000,000
Single-Family [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	2,221,000,000	3,105,000,000
Provision (benefit) for loan losses	(147,000,000)	38,000,000
Charge-offs	(19,000,000)	(101,000,000)
Recoveries	8,000,000	71,000,000
Transfers	(359,000,000)	(420,000,000)
Other	51,000,000	9,000,000
Ending balance	1,755,000,000	2,702,000,000
Multifamily [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	364,000,000	539,000,000
Provision (benefit) for loan losses	(50,000,000)	(28,000,000)
Charge-offs	(15,000,000)	(51,000,000)
Other	7,000,000	3,000,000
Ending balance	306,000,000	463,000,000
Multifamily [Member] | Fannie Mae [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	161,000,000	319,000,000
Provision (benefit) for loan losses	(37,000,000)	(12,000,000)
Charge-offs	(15,000,000)	(51,000,000)
Other	5,000,000	2,000,000
Ending balance	114,000,000	258,000,000
Multifamily [Member] | Consolidated Trusts [Member]
Allowance for Loan Losses [Roll Forward]
Beginning balance	203,000,000	220,000,000
Provision (benefit) for loan losses	(13,000,000)	(16,000,000)
Charge-offs	0	0
Other	2,000,000	1,000,000
Ending balance	$ 192,000,000	$ 205,000,000