Securities (Gains and Losses Recognized in Income from Available-for-Sale and Trading Securities) (Parenthetical) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Investment Holdings
Total trading debt securities gains (losses)	[1]	$ (4)	$ 2	$ (18)	$ 3
Total equity securities gains (losses)	[2],[3]	(5)	2	(8)	3
Equity securities unrealized gains (losses)		(5)	2	(6)	3
Corporate Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings
Total trading debt securities gains (losses)				(2)
Interest-Only Mortgage-Backed Securities
Investment Holdings
Net gains/losses on interest-only mortgage-backed securities		$ 0	$ (2)	$ 1	$ (1)

[1] Includes an immaterial net loss and a net loss of $ 2 for the three and six months ended June 30, 2018 , respectively, and immaterial net gains for both the three and six months ended June 30, 2017 , respectively, recorded in corporate banking

[2] Includes net unrealized losses of $ 5 and $ 6 for the three and six months ended June 30, 2018 , respectively, and net unrealized gains of $ 2 and $ 3 for the three and six months ended June 30, 2017 , respectively.

[3] Includes immaterial net gains for both the three and six months en ded June 30, 2018 and 2017 recorded in corporate banking revenue and wealth and asset management revenue in the Condensed Consolidated Statements of Income.