Mortgage Loans Credit Quality Indicators - MF (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
Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	330,618	295,664
Multifamily [Member] | Non-classified [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	323,773	289,231
Multifamily [Member] | Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	5	1
Multifamily [Member] | Total classified [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	$ 6,845	$ 6,433