Consolidations and Transfers of Financial Assets - Transfers of Financial Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 197,100	$ 202,900	$ 413,900	$ 291,900
Unconsolidated VIEs
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	144	$ 170	287	$ 351
Unconsolidated VIEs | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	1,200		1,200		$ 1,700
Retained interests: fair value	$ 2,300		$ 2,300		$ 2,900