Discontinued Operations - Schedule of Derivative Gain (Loss) Amounts Recognized in Income (Detail) (Discontinued Operations [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Discontinued Operations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Reclassification of mark-to-market to realized on settlement of contracts	$ 10	$ 27
Unrealized mark-to-market loss		(3)	(30)
Total net gain (loss)	$ 10	$ 24	$ (30)