Securitizations and Financings - Securitization Trusts (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entities and Securitizations [Abstract]
Total collateral balances - UPB	$ 1,171	$ 1,326
Total certificate balances	1,172	1,329
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Unconsolidated securitization trusts	$ 140	$ 154