Discontinued Operations - Activity of Energy Commodity Contracts Designated as Cash Flow Hedges (Parenthetical) (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 reclassified from AOCL to income from discontinued operations	$ 0	$ 0	$ 4	$ 0