Discontinued Operations - Activity of Energy Commodity Contracts Designated as Cash Flow Hedges (Detail) (Discontinued Operations [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Discontinued Operations [Member]
Derivatives And Hedging Activities [Line Items]
Amount of net pre-tax loss arising during the period included in Accumulated Other Comprehensive Loss
Income from Discontinued operations, Net of Income Taxes	2	12	10	25
Total net pre-tax loss reclassified into Income from Discontinued operations, Net of Income Taxes	2	12	10	25
Net pre-tax gain on commodity derivatives included in Accumulated Other Comprehensive Loss	$ 2	$ 12	$ 10	$ 25