Derivative Instruments and Hedging Activities - Commodity Derivative Activity in Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Unrealized gain (loss) on derivatives at beginning of period, Before tax	$ 1	$ (10)
Realized amounts reclassified into earnings, Before tax		9
Net change in derivative fair value, Before tax	(1)	(11)
Unrealized gain (loss) on derivatives at end of period, Before tax		(12)
Unrealized gain (loss) on derivatives at beginning of period, After tax	1	(6)
Realized amounts reclassified into earnings, After tax		6
Net change in derivative fair value, After tax	(1)	(8)
Unrealized gain on derivatives at end of period, After tax		$ (8)