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	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Long-term debt	$ 2,737	$ 2,822
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	4,169	4,554
Long-term debt, Estimated fair value	4,002	4,351
Loans Unpaid Principal Balance	2,450	2,618
Long Term Debt Unpaid Principal Balance	$ 3,604	$ 3,800