Derivative Instruments and Hedging Activities - Commodity Derivative Activity Recorded in Statement of Consolidated Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 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	$ (11)	$ 78	$ (20)	$ 119
Derivative Instrument Gains (Losses), Net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) for ineffectiveness on cash flow hedges
Gain (loss) on derivatives not designated as cash flow hedges	$ 247		$ 147