Securities (Other Than Temporary Impairment Recognized) (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 | Equity securities
Investments, Unrealized Loss Position
OTTI		0	(1)
Available-for-sale securities | Debt securities
Investments, Unrealized Loss Position
OTTI		$ (10)	$ (2)

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