Special Purpose Entities, Including Variable Interest Entities - Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Long-term debt	$ 2,749	$ 2,822
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member]
Variable Interest Entities [Line Items]
Loans Unpaid Principal Balance	2,399	2,618
Long Term Debt Unpaid Principal Balance	$ 3,506	$ 3,800