Gross Unrealized Losses and Fair Value of Investment Securities (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
12 months or more, Gross unrealized losses	$ 171	$ 172	[1]
Gross unrealized losses	603	289	[1]
Other-than-temporary impairments
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
12 months or more, Gross unrealized losses		1
Gross unrealized losses		1
Below investment grade
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
12 months or more, Gross unrealized losses	66	27	[1],[2]
Gross unrealized losses	$ 166	69	[1],[2]
Below investment grade | Other-than-temporary impairments
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
12 months or more, Gross unrealized losses		$ 1

[1] Amounts included $1 million of unrealized losses on other-than-temporarily impaired securities.

[2] Amounts that have been in a continuous unrealized loss position for 12 months or more included $1 million of unrealized losses on other-than-temporarily impaired securities.