Securities (Gains and Losses Recognized in Income from Available-for-Sale and Trading Securities) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Securities
OTTI	[1]	$ (4)	$ (2)	$ (28)	$ (8)
Net realized gains (losses) on available-for-sale and other securities		(1)	2	(3)	18
Total trading securities gains (losses)		5	2	11	2
Total available for sale and trading securities gains (losses) recognized in income		4	4	8	20
Available-for-sale Securities
Securities
Realized gains		24	13	53	42
Realized losses		(21)	(9)	(28)	(16)
OTTI		$ (4)	$ (2)	$ (28)	$ (8)

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