Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loans Receivable, Net [Abstract]
Other loans included in impaired loans apart from TDR loans	$ 171	$ 237
Residential mortgage loan carried at lower of amortized cost or fair value less cost to sell		445
Non Accrual loans included in TDR loan	$ 416	$ 519