Mortgage Loans Loans in Mortgage Portfolio (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 3,013,878,000,000		$ 3,013,878,000,000			$ 3,010,753,000,000
Cost basis and fair value adjustments, net	39,790,000,000		39,790,000,000			36,842,000,000
Allowance for loan losses for loans held for investment	(23,799,000,000)	$ (31,150,000,000)	(23,799,000,000)	$ (31,150,000,000)	$ (25,819,000,000)	(27,951,000,000)	$ (31,820,000,000)	$ (35,541,000,000)
Total mortgage loans	3,029,869,000,000		3,029,869,000,000			3,019,644,000,000
Carrying value of loans redesignated from HFI to HFS	1,000,000,000	4,300,000,000	1,600,000,000	4,600,000,000
Sale of loans, unpaid principal balance	1,500,000,000	633,000,000	2,600,000,000	633,000,000
Single-family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,803,200,000,000		2,803,200,000,000			2,812,411,000,000
Recorded investment of single-family mortgage loans referred to foreclosure	21,500,000,000		21,500,000,000			25,600,000,000
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	210,678,000,000		210,678,000,000			198,342,000,000
Fannie Mae [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	240,507,000,000		240,507,000,000			251,336,000,000
Cost basis and fair value adjustments, net	(12,202,000,000)		(12,202,000,000)			(12,939,000,000)
Allowance for loan losses for loans held for investment	(22,793,000,000)	(29,724,000,000)	(22,793,000,000)	(29,724,000,000)	(24,557,000,000)	(26,510,000,000)	(29,873,000,000)	(33,117,000,000)
Total mortgage loans	205,512,000,000		205,512,000,000			211,887,000,000
Fannie Mae [Member] | Single-family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	228,866,000,000		228,866,000,000			238,237,000,000
Fannie Mae [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	11,641,000,000		11,641,000,000			13,099,000,000
Consolidated Trusts [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,773,371,000,000		2,773,371,000,000			2,759,417,000,000
Cost basis and fair value adjustments, net	51,992,000,000		51,992,000,000			49,781,000,000
Allowance for loan losses for loans held for investment	(1,006,000,000)	$ (1,426,000,000)	(1,006,000,000)	$ (1,426,000,000)	$ (1,262,000,000)	(1,441,000,000)	$ (1,947,000,000)	$ (2,424,000,000)
Total mortgage loans	2,824,357,000,000		2,824,357,000,000			2,807,757,000,000
Consolidated Trusts [Member] | Single-family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,574,334,000,000		2,574,334,000,000			2,574,174,000,000
Consolidated Trusts [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 199,037,000,000		$ 199,037,000,000			$ 185,243,000,000