Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Receivables [Abstract]
Other loans included in impaired loans apart from TDR loans	$ 85	$ 92
Residential Mortgage Loan TDR Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell	763	706	608
Non Accrual loans included in TDR loan	$ 485	$ 528