Securities (Realized Gains and Losses Recognized in Income from Available-for-Sale Securities) (Detail) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Investments, Unrealized Loss Position
OTTI	[1]	$ 3,000,000	$ 4,000,000	$ 5,000,000	$ 5,000,000
Available-for-sale Securities
Investments, Unrealized Loss Position
Realized gains		15,000,000	29,000,000	29,000,000	44,000,000
Realized losses		(4,000,000)	(31,000,000)	(8,000,000)	(33,000,000)
OTTI		(3,000,000)	(4,000,000)	(5,000,000)	(5,000,000)
Net realized gains (losses)	[2]	$ 8,000,000	$ (6,000,000)	$ 16,000,000	$ 6,000,000

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

[2] (a) Excludes n et losses on interest-only mortgage- backed securities of $ 3 and $ 8 for the three and six months ended June 30, 2016 , respectively, and net gains on interest-onl y mortgage-backed securities of $ 11 and $ 2 for the three and six months ended June 30, 2015 , respectively.