Mortgage Loans Credit Quality Indicators - SF (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	$ 3,336,929	$ 3,255,168
Single-Family [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	3,006,311	2,959,504
Single-Family [Member] | Primary [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	2,936,621	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	2,556,685	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	243,459	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	131,653	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	4,824	9,337
Single-Family [Member] | Alt-A [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	42,255	53,271
Single-Family [Member] | Alt-A [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	37,932	45,476
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, Credit Quality Indicator [Line Items]
Total recorded investment	2,225	3,804
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, Credit Quality Indicator [Line Items]
Total recorded investment	1,078	1,997
Single-Family [Member] | Alt-A [Member] | Estimated mark-to-market loan-to-value ratio greater than 100% [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	1,020	1,994
Single-Family [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	10,306	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	9,002	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	642	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	318	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	344	707
Single-Family [Member] | Government [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	$ 17,129	$ 22,130