Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Receivables [Abstract]
Balance at beginning of period	$ 45	$ 37	$ 35	$ 37
Provision (credit) for losses on lending-related commitments	9	(2)	19	(2)
Balance at end of period	$ 54	$ 35	$ 54	$ 35