Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Receivables [Abstract]
Residential Mortgage Loan TDR Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell	$ 741	$ 706	$ 687