Composition of the Company's Loan Portfolio (Additional Information) (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	[1]	$ 143,181	$ 143,298
Loans Receivable, Fair Value Disclosure		196	222
Loans Held-for-sale, Fair Value Disclosure		1,577	3,540
Finance Leases Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		3,740	3,693
Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		778	729
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		67,704	65,074
Loans Receivable, Fair Value Disclosure		$ 196	$ 222

[1] Includes loans of consolidated VIEs of $179 million and $211 million at December 31, 2017 and December 31, 2016, respectively.