Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (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
Disclosure Asset Quality Changes In Liability For Credit Losses On Lending Related Commitments [Abstract]
Balance at beginning of period	$ 32	$ 45	$ 29	$ 45
Provision (credit) for losses on lending-related commitments	5	6	8	6
Balance at end of period	$ 37	$ 51	$ 37	$ 51