Realized Gains and Losses Recognized in Income from Available-for-Sale Securities (Detail) - Available-for-sale Securities - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Investments, Unrealized Loss Position [Line Items]
Realized gains		$ 29	$ 14	$ 44	$ 41
Realized losses		(31)		(33)	(5)
OTTI		(4)		(5)	(17)
Net realized gains (losses)	[1]	$ (6)	$ 14	$ 6	$ 19

[1] Excludes net gains on interest-only mortgage-backed securities of $11 and $2 for the three and six months ended June 30, 2015, respectively, and net losses on interest-only mortgage-backed securities of $8 and $7 for the three and six months ended June 30, 2014, respectively.