Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Receivables [Abstract]
Other loans included in impaired loans apart from TDR loans	$ 62	$ 85
Residential Mortgage Loan TDR Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell	858	763	$ 741
Non Accrual loans included in TDR loan	$ 520	$ 485