Securities (Other Than Temporary Impairment Recognized) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Unrealized Loss Position
OTTI	[1]	$ (54)	$ (16)	$ (5)
Available-for-sale securities | Equity securities
Investments, Unrealized Loss Position
OTTI		0	(1)	0
Available-for-sale securities | Debt securities
Investments, Unrealized Loss Position
OTTI		$ (54)	$ (15)	$ (5)

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