Composition of the Company's Loan Portfolio (Additional Information) (Detail) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	[1]	$ 142,618	$ 143,181
Loans Receivable, Fair Value Disclosure		188	196
Loans Held-for-sale, Fair Value Disclosure		1,428	1,577
Finance Leases Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		3,577	3,693
Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		788	778
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		67,294	67,704
Loans Receivable, Fair Value Disclosure		$ 188	$ 196

[1] Includes loans of consolidated VIEs of $171 million and $179 million at March 31, 2018 and December 31, 2017, respectively.