Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 3,043,761	$ 3,035,712
Single-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,831,002	2,835,538
Single-family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,669,586	2,662,193
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	2,279,064	2,228,533
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	238,897	250,373
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	104,938	122,939
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	21,829	27,875
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	11,218	14,625
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	3,459	4,520
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	10,181	13,328
Single-family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	89,144	96,101
Single-family [Member] | Alt-A [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	58,301	59,000
Single-family [Member] | Alt-A [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	11,003	12,588
Single-family [Member] | Alt-A [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	7,907	9,345
Single-family [Member] | Alt-A [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	5,066	6,231
Single-family [Member] | Alt-A [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	2,951	3,730
Single-family [Member] | Alt-A [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	946	1,260
Single-family [Member] | Alt-A [Member] | Estimated mark-to-market loan-to-value ratio greater than 125% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,970	3,947
Single-family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	33,095	36,410
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	20,834	21,274
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	4,225	4,936
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	3,162	3,861
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	2,076	2,596
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	1,216	1,592
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	391	545
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	1,191	1,606
Single-family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 39,177	$ 40,834