Derivative Instruments and Hedging Activities - Commodity Derivative Activity Recorded in Statement of Consolidated Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Oil and Gas Production Revenues [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on cash flow hedges reclassified from accumulated other comprehensive loss	$ (9)	$ 41
Revenues and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) for ineffectiveness on cash flow hedges		(1)
Gain (loss) on derivatives not designated as cash flow hedges	$ (100)