Allowance for Credit Losses - Analysis of Allowance for Credit Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 647		$ 743
Provision for credit losses	21	[1]	0	[1]
Charge-offs	(110)		(162)
Recoveries	10		22
Balance at end of period	$ 568		$ 603

[1] The provision assigned to the segments is based on the segments’ net charge offs and the change in allowance for credit losses.