Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,095,816	$ 3,035,712
Single-Family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,863,935	2,835,538
Single-Family [Member] | Primary [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	2,715,497	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	2,321,201	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	244,231	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	114,412	122,939
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	35,653	60,348
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	81,947	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	56,250	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	9,787	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	6,731	9,345
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	9,179	15,168
Single-Family [Member] | Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	29,343	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	19,382	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	3,657	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	2,627	3,861
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	3,677	6,339
Single-Family [Member] | Government [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 37,148	$ 40,834