Securities (Gains and Losses Recognized in Income from Trading Securities) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Securities
Realized gains		$ 85	$ 72	$ 97
Realized losses		34	45	76
OTTI	[1]	54	16	5
Net realized gains (losses) on available-for-sale and other securities		(3)	11	16
Total trading securities gains (losses)		10	0	(7)
Total Available For Sale And Trading Securities Gains Losses		$ 7	$ 11	$ 9

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