LHFI by Credit Quality Indicator (Additional Information) (Detail) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	[1]	$ 133,560	$ 133,112
Federal National Mortgage Association (FNMA) Insured Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		627	632
Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross		$ 4,588	$ 4,827

[1] Includes loans of consolidated VIEs of $256 million and $288 million at September 30, 2015 and December 31, 2014, respectively.