Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 3,039,240	$ 3,047,794
Single-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,840,541	2,858,561
Single-family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,660,245	2,656,220
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,248,367	2,156,165
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	240,860	261,709
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	108,540	140,778
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% and less than or equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	28,684	43,014
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 110% and less than or equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	15,115	23,439
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 120% and less than or equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	4,706	7,529
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	13,973	23,586
Single-family [Member] | Alt-A
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	100,349	112,761
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	61,367	60,851
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	13,188	15,151
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	9,758	12,490
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio greater than 100% and less than or equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	6,528	8,998
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio greater than 110% and less than or equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	4,018	6,033
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio greater than 120% and less than or equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	1,295	2,114
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio greater than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	4,195	7,124
Single-family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	38,228	44,259
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	22,263	22,558
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 80% and less than or equal to 90% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	5,197	6,046
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 90% and less than or equal to 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	4,020	5,236
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% and less than or equal to 110% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,787	3,900
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 110% and less than or equal to 120% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	1,699	2,615
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 120% and less than or equal to 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	552	904
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	1,710	3,000
Single-family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 41,719	$ 45,321