Mortgage Loans Loans in Mortgage Portfolio (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 3,008,127,000,000		$ 3,019,300,000,000
Cost basis and fair value adjustments, net	36,809,000,000		35,735,000,000
Allowance for loan losses for loans held for investment	(31,820,000,000)	(41,911,000,000)	(35,541,000,000)	(43,846,000,000)
Total mortgage loans	3,013,116,000,000		3,019,494,000,000
Carrying value of loans redesignated from HFI to HFS	330,000,000	2,200,000,000
Sale of loans, unpaid principal balance	0	1,000,000,000
Minimum Days Past Due of Single Family Nonaccrual Loans 1			60 days
Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,817,111,000,000		2,832,000,000,000
Recorded investment of mortgage loans referred to foreclosure	32,300,000,000
Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	191,016,000,000		187,300,000,000
Fannie Mae [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	279,064,000,000		285,371,000,000
Cost basis and fair value adjustments, net	(12,775,000,000)		(12,705,000,000)
Allowance for loan losses for loans held for investment	(29,873,000,000)	(39,004,000,000)	(33,117,000,000)	(40,521,000,000)
Total mortgage loans	236,416,000,000		239,549,000,000
Fannie Mae [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	258,350,000,000		262,116,000,000
Fannie Mae [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	20,714,000,000		23,255,000,000
Consolidated Trusts [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,729,063,000,000		2,733,929,000,000
Cost basis and fair value adjustments, net	49,584,000,000		48,440,000,000
Allowance for loan losses for loans held for investment	(1,947,000,000)	(2,907,000,000)	(2,424,000,000)	(3,325,000,000)
Total mortgage loans	2,776,700,000,000		2,779,945,000,000
Consolidated Trusts [Member] | Single-Family [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	2,558,761,000,000		2,569,884,000,000
Consolidated Trusts [Member] | Multifamily [Member]
Loans in Mortgage Portfolio [Line Items]
Unpaid principal balance of mortgage loans	$ 170,302,000,000		$ 164,045,000,000