Derivative Instruments and Hedging Activities (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	$ 59		$ 59		$ 47
Derivative Liability, Fair Value	21		21		83
Realized Mark-to-Market (Gain) Loss	4	(22)	28	(39)
Unrealized Mark-to-Market (Gain) Loss	131	(300)	(74)	(140)
Total (Gain) Loss on Commodity Derivative Instruments	135	(322)	(46)	(179)
Current Assets | Commodity Contract
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	35		35		10
Current Liabilities | Commodity Contract
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	16		16		76
Noncurrent Assets | Commodity Contract
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	24		24		37
Noncurrent Liabilities | Commodity Contract
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	$ 5		$ 5		$ 7