Realized Gains and Losses Recognized in Income from Available-for-Sale Securities (Detail) (Available-for-sale Securities, USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Available-for-sale Securities
Investments, Unrealized Loss Position [Line Items]
Realized gains	$ 16		$ 14		$ 58		$ 54
Realized losses	(4)		(4)		(9)		(90)
OTTI	(7)		(45)		(24)		(57)
Net realized gains (losses)	$ 5	[1]	$ (35)	[1]	$ 25	[1]	$ (93)	[1]

[1] Excludes net losses on interest-only mortgage-backed securities of $1 and $9 for the three and nine months ended September 30, 2014, respectively, and net gains on interest-only mortgage-backed securities of $40 and $121 for the three and nine months ended September 30, 2013, respectively.