Consolidations and Transfers of Financial Assets - Transfers of Financial Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 140,100	$ 213,000	$ 554,000	$ 504,900
Unconsolidated VIEs
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	139	$ 166	426	$ 517
Unconsolidated VIEs | Single Class MBS, REMIC & Megas
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	1,100		1,100		$ 1,700
Retained interests: fair value	$ 2,100		$ 2,100		$ 2,900