Realized Gains and Losses Recognized in Income from Available-for-Sale Securities (Detail) - Available-for-sale Securities - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Unrealized Loss Position [Line Items]
Realized gains		$ 97	$ 70	$ 77
Realized losses		(76)	(9)	(102)
OTTI		(5)	(24)	(74)
Net realized gains (losses)	[1]	$ 16	$ 37	$ (99)

[1] Excludes net losses on interest-only mortgage-backed securities of $4 and $17 for the years ended December 31, 2015 and 2014, respectively, and net gains on interest-only mortgage-backed securities of $129 for the year ended December 31, 2013.