Derivative Instruments and Hedging Activities (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Asset Derivative Instruments	$ 84	$ 47
Liability Derivative Instruments	10	83
Summary of Derivative Instruments Impact on Results of Operations [Abstract]
Realized Mark-to-Market (Gain) Loss	34	(64)	(87)
Unrealized Mark-to-Market (Gain) Loss	(109)	22	(70)
Total (Gain) Loss on Commodity Derivative Instruments	(75)	(42)	(157)
Current Assets
Derivatives, Fair Value [Line Items]
Asset Derivative Instruments	63	10
Current Liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Instruments	7	76
Noncurrent Assets
Derivatives, Fair Value [Line Items]
Asset Derivative Instruments	21	37
Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Instruments	$ 3	$ 7