Variable Interest Entities - Supplemental Information about Loans Held as Assets and Long-Term Debt Associated with Consolidated Variable Interest Entities (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entities [Line Items]
Loans, Unpaid principal balance		$ 19	$ 19
Variable Interest Entity, Consolidated, Carrying Amount, Liabilities	$ 364
Variable Interest Entities [Member]
Variable Interest Entities [Line Items]
Loans, Unpaid principal balance	2,618	3,418
Long-term debt, Unpaid principal balance	$ 3,800	$ 4,553