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	Mar. 31, 2021	Dec. 31, 2020
Variable Interest Entities [Line Items]
Long-term debt	$ 2,661	$ 2,739
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	4,427	4,493
Long-term debt, Estimated fair value	4,264	4,324
Loans Unpaid Principal Balance	2,519	2,546
Long Term Debt Unpaid Principal Balance	$ 3,758	$ 3,769