Securities (Gains and Losses Recognized in Income from Available-for-Sale and Trading Securities) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investment Holdings
Total trading debt securities gains (losses)	$ (14)	$ 1
Total equity securities gains (losses)	(3)	1
Equity securities unrealized gains (losses)	(2)	1
Corporate Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings
Total trading debt securities gains (losses)	(1)	1
Interest-Only Mortgage-Backed Securities
Investment Holdings
Net gains/losses on interest-only mortgage-backed securities	$ 1	$ 1