Asset Quality - Changes in Liability for Credit Losses on Lending Related Commitments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 50	$ 45	$ 56	$ 35
Provision (credit) for losses on lending-related commitments	3	9	(3)	19
Balance at end of period	$ 53	$ 54	$ 53	$ 54