Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 3,136,729	$ 3,095,816
Single-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,890,101	2,863,935
Single-family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,754,975	2,715,497
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	2,410,185	2,321,201
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	231,412	244,231
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	88,637	114,412
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	24,741	35,653
Single-family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	74,399	81,947
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	54,917	56,250
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	8,010	9,787
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	5,088	6,731
Single-family [Member] | Alt-A [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	6,384	9,179
Single-family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	25,347	29,343
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	18,219	19,382
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	2,826	3,657
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	1,908	2,627
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	2,394	3,677
Single-family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment in loans	$ 35,380	$ 37,148