Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	$ 3,311,698	$ 3,255,168
Single-family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	2,990,501	2,959,504
Single-family [Member] | Primary [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	2,917,020	2,869,265
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	2,569,771	2,521,766
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, Credit Quality Indicator [Line Items]
Total recorded investment in loans	228,868	228,614
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, Credit Quality Indicator [Line Items]
Total recorded investment in loans	113,424	109,548
Single-family [Member] | Primary [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	4,957	9,337
Single-family [Member] | Alt-A
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	44,287	53,271
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	39,710	45,476
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, Credit Quality Indicator [Line Items]
Total recorded investment in loans	2,365	3,804
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, Credit Quality Indicator [Line Items]
Total recorded investment in loans	1,131	1,997
Single-family [Member] | Alt-A | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	1,081	1,994
Single-family [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	11,105	14,838
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio less than or equal to 80% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	9,694	12,291
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, Credit Quality Indicator [Line Items]
Total recorded investment in loans	709	1,195
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, Credit Quality Indicator [Line Items]
Total recorded investment in loans	337	645
Single-family [Member] | Other [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	365	707
Single-family [Member] | Government [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment in loans	$ 18,089	$ 22,130