Mortgage Loans Credit Quality Indicators - MF (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	$ 3,662,711	$ 3,336,929
Financing Receivable, before Allowance for Credit Loss (includes $6,490 and $7,825, respectively, at fair value)	3,659,247	3,336,405
Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment	377,426	330,618
Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	72,014
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	44,753
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	74,183
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	69,337
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	63,616
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	53,523
Financing Receivable, before Allowance for Credit Loss (includes $6,490 and $7,825, respectively, at fair value)	377,426
Pass | Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment		323,773
Pass | Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	71,977
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	43,174
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	70,933
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	68,296
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	62,087
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	50,907
Financing Receivable, before Allowance for Credit Loss (includes $6,490 and $7,825, respectively, at fair value)	367,374
Criticized | Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total recorded investment		6,845
Criticized | Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, Year One, Originated, Current Fiscal Year	37
Financing Receivable, Year Five, Originated, Four Years before Current Fiscal Year	1,579
Financing Receivable, Originated, More than Five Years before Current Fiscal Year	3,250
Financing Receivable, Year Two, Originated, Fiscal Year before Current Fiscal Year	1,041
Financing Receivable, Year Three, Originated, Two Years before Current Fiscal Year	1,529
Financing Receivable, Year Four, Originated, Three Years before Current Fiscal Year	2,616
Financing Receivable, before Allowance for Credit Loss (includes $6,490 and $7,825, respectively, at fair value)	10,052
Doubtful [Member] | Multifamily [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing Receivable, before Allowance for Credit Loss (includes $6,490 and $7,825, respectively, at fair value)	$ 1	$ 5