Derivative Instruments and Hedging Activities - Commodity Derivative Activity in Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 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	20
Net change in derivative fair value, Before tax			(1)	0
Unrealized gain on derivatives at end of period, Before tax	0	10	0	10
Unrealized gain (loss) on derivatives at beginning of period, After tax			1	(6)
Realized amounts reclassified into earnings, After tax			0	14
Net change in derivative fair value, After tax	0	7	(1)	(1)
Unrealized gain on derivatives at end of period, After tax	$ 0	$ 7	$ 0	$ 7