Derivative Instruments and Hedging Activities - Commodity Derivative Activity in Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 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		0	18
Net change in derivative fair value, Before tax		(1)	(7)
Ineffectiveness reclassified into earnings, Before tax		0	1
Unrealized gain on derivatives at end of period, Before tax	2	0	2
Unrealized gain (loss) on derivatives at beginning of period, After tax		1	(6)
Realized amounts reclassified into earnings, After tax		0	13
Net change in derivative fair value, After tax	(5)	(1)	(6)
Ineffectiveness reclassified into earnings, After tax	1	0	1
Unrealized gain on derivatives at end of period, After tax	$ 2	$ 0	$ 2