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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investment Holdings
Total trading debt securities gains (losses)	$ (1)	$ 2	$ (20)	$ 5
Total equity securities gains (losses)	(6)	3	(13)	6
Equity securities unrealized gains (losses)	(6)	2	(12)	4
Corporate Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings
Total trading debt securities gains (losses)		1	(2)	1
Interest-Only Mortgage-Backed Securities
Investment Holdings
Net gains/losses on interest-only mortgage-backed securities	$ 0	$ (1)	$ 1	$ (2)