Securities (Gains and Losses Recognized in Income from Available-for-Sale and Trading Securities) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investment Holdings
Total trading securities gains (losses)	$ 5	$ 2	$ 11	$ 2
Corporate Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings
Total trading securities gains (losses)	1		1	(1)
Interest-Only Mortgage-Backed Securities
Investment Holdings
Net gains/losses on interest-only mortgage-backed securities	$ (1)		$ (2)	$ (8)