Mortgage Loans Credit Quality Indicators - MF (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 3,255,168,000,000	$ 3,189,975,000,000
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	295,664,000,000	267,001,000,000
Multifamily [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	289,231,000,000	263,416,000,000
Multifamily [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	1,000,000	0
Multifamily [Member] | Total classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Total recorded investment	$ 6,433,000,000	$ 3,585,000,000