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) - Variable Interest Entities [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entities [Line Items]
Loans Unpaid Principal Balance	$ 2,439	$ 2,618
Long Term Debt Unpaid Principal Balance	$ 3,550	$ 3,800