Discontinued Operations - Cash Flow Hedges Included in Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax	$ 9	$ 10
Portion Expected to be Reclassified to Income during the Next 12 Months	1	1
Discontinued Operations [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax		15
Portion Expected to be Reclassified to Income during the Next 12 Months		13
Discontinued Operations [Member] | Energy Commodity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax		15
Portion Expected to be Reclassified to Income during the Next 12 Months		$ 13
Maximum Term		23 months