Allowance for Credit Losses - Analysis of Allowance for Credit Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Loans Receivable [Line Items]
Balance at beginning of period	$ 619	$ 747	$ 743	$ 852
Provision for credit losses	84	78	173	171
Charge-offs	(76)	(75)	(329)	(300)
Recoveries	10	29	50	56
Allowance on loans transferred to held for sale		(30)		(30)
Balance at end of period	$ 637	$ 749	$ 637	$ 749