Derivative Instruments- Impact of Derivative Instruments on Balance Sheet (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Master netting agreements, cash collateral received	$ 1,122	$ 1,841
Master netting agreements, cash collateral paid	$ 616	$ 456