LHFI by Credit Quality Indicator (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 and Leases Receivable, Impaired, Commitment to Lend		2	2
Federal National Mortgage Association (FNMA) Insured Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		611	560
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		$ 6,693	$ 6,633

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