Derivatives Not Designated as Hedging Instruments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	$ 2	$ 0	$ 4	$ (19)
Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	(36)	848	794	477
Not designated as hedging instruments | Commodity contracts | Natural gas, oil and NGL sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	(36)	851	796	491
Not designated as hedging instruments | Interest rate contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	$ 0	$ (3)	$ (2)	$ (14)