Securities (Other Than Temporary Impairment Recognized) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investments, Unrealized Loss Position
OTTI	[1]	$ (4)	$ (2)	$ (28)	$ (8)
Available-for-sale securities | Equity securities
Investments, Unrealized Loss Position
OTTI		0	0	0	(1)
Available-for-sale securities | Debt securities
Investments, Unrealized Loss Position
OTTI		$ (4)	$ (2)	$ (28)	$ (7)

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