Realized Gains and Losses Recognized in Income from Available-for-Sale Securities (Detail) - Available-for-sale Securities - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investments, Unrealized Loss Position [Line Items]
Realized gains		$ 35	$ 16	$ 79	$ 58
Realized losses		(25)	(4)	(58)	(9)
OTTI			(7)	(5)	(24)
Net realized gains (losses)	[1]	$ 10	$ 5	$ 16	$ 25

[1] Excludes net losses on interest-only mortgage-backed securities of $7 and $4 for the three and nine months ended September 30, 2015, respectively, and net losses on interest-only mortgage-backed securities of $1 and $9 for the three and nine months ended September 30, 2014, respectively.