Allowance for Credit Losses - Analysis of Allowance for Credit Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 568		$ 603		$ 647		$ 743
Provision for credit losses	67	[1]	89	[1]	88	[1]	89	[1]
Charge-offs	(48)		(91)		(158)		(253)
Recoveries	18		18		28		40
Balance at end of period	$ 605		$ 619		$ 605		$ 619

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