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
	Mar. 31, 2015		Mar. 31, 2014
Available-for-sale Securities
Investments, Unrealized Loss Position [Line Items]
Realized gains	$ 15		$ 27
Realized losses	(2)		(5)
OTTI	(1)		(17)
Net realized gains (losses)	$ 12	[1]	$ 5	[1]

[1] Excludes net losses on interest-only mortgage-backed securities of $9 for the three months ended March 31, 2015 and net gains on interest-only mortgage-backed securities of $1 for the three months ended March 31, 2014