Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Other loans included in impaired loans apart from TDR loans	$ 378	$ 614
Non Accrual loans included in TDR loan	$ 525	$ 331