Special Purpose Entities, Including Variable Interest Entities - Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entities [Line Items]
Long-term debt	$ 2,671	$ 2,739
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	4,434	4,493
Long-term debt, Estimated fair value	4,270	4,324
Loans Unpaid Principal Balance	2,486	2,546
Long Term Debt Unpaid Principal Balance	$ 3,727	$ 3,769