Securities (Realized Gains and Losses Recognized in Income from Available-for-Sale Securities) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Investments, Unrealized Loss Position
OTTI	[1]	$ (10)	$ (3)
Available-for-sale Securities
Investments, Unrealized Loss Position
Realized gains		9	15
Realized losses		(1)	(4)
OTTI		(10)	(3)
Net realized gains (losses)	[2]	$ (2)	$ 8

[1] (a) Included in securities gains, net, in the Condensed Consolidated Statements of Income

[2] (a) Excludes net gains of $ 1 and net losses of $ 6 on interest-only mortgage-backed securities for the three months ended March 31, 201 7 and 20 1 6, respectively.