Mortgage Loans Loans in Mortgage Portfolio (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2013
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 3,012,689,000,000		$ 3,012,689,000,000		$ 3,019,300,000,000
Cost basis and fair value adjustments, net	36,902,000,000		36,902,000,000		35,735,000,000
Allowance for loan losses for loans held for investment	(29,135,000,000)	$ (36,931,000,000)	(29,135,000,000)	$ (36,931,000,000)	(35,541,000,000)	$ (31,150,000,000)	$ (39,067,000,000)	$ (43,846,000,000)
Total mortgage loans	3,020,456,000,000		3,020,456,000,000		$ 3,019,494,000,000
Carrying value of loans redesignated from HFI to HFS	1,300,000,000	0	5,900,000,000	2,200,000,000
Financing Receivable, Reclassification to Held-for-investment		240,000,000		241,000,000
Sale of loans, unpaid principal balance	1,900,000,000	0	$ 2,500,000,000	1,900,000,000
Minimum days past due of single family nonaccrual loans			60 days		60 days
Single-family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,815,884,000,000		$ 2,815,884,000,000		$ 2,832,000,000,000
Recorded investment of single-family mortgage loans referred to foreclosure	27,600,000,000		27,600,000,000
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	196,805,000,000		196,805,000,000		187,300,000,000
Fannie Mae [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	257,768,000,000		257,768,000,000		285,371,000,000
Cost basis and fair value adjustments, net	(12,789,000,000)		(12,789,000,000)		(12,705,000,000)
Allowance for loan losses for loans held for investment	(27,655,000,000)	(34,562,000,000)	(27,655,000,000)	(34,562,000,000)	(33,117,000,000)	(29,724,000,000)	(36,643,000,000)	(40,521,000,000)
Total mortgage loans	217,324,000,000		217,324,000,000		239,549,000,000
Fannie Mae [Member] | Single-family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	242,496,000,000		242,496,000,000		262,116,000,000
Fannie Mae [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	15,272,000,000		15,272,000,000		23,255,000,000
Consolidated Trusts [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,754,921,000,000		2,754,921,000,000		2,733,929,000,000
Cost basis and fair value adjustments, net	49,691,000,000		49,691,000,000		48,440,000,000
Allowance for loan losses for loans held for investment	(1,480,000,000)	$ (2,369,000,000)	(1,480,000,000)	$ (2,369,000,000)	(2,424,000,000)	$ (1,426,000,000)	$ (2,424,000,000)	$ (3,325,000,000)
Total mortgage loans	2,803,132,000,000		2,803,132,000,000		2,779,945,000,000
Consolidated Trusts [Member] | Single-family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,573,388,000,000		2,573,388,000,000		2,569,884,000,000
Consolidated Trusts [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 181,533,000,000		$ 181,533,000,000		$ 164,045,000,000