Securities (Gains and Losses Recognized in Income from Trading Securities) (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investment Holdings
Total trading securities gains (losses)	$ 10	$ 0	$ (7)
Corporate Banking Revenue and Wealth and Asset Management Revenue [Member]
Investment Holdings
Total trading securities gains (losses)	1	(3)	(4)
Interest-Only Mortgage Backed Securities
Investment Holdings
Net gains/losses on interest-only mortgage-backed securities	$ (2)	$ (4)	$ (4)