Derivative Instruments and Hedging Activities (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	$ 49			$ 84
Derivative Liability, Fair Value	53			10
Realized Mark-to-Market (Gain) Loss	(7)		23
Total Unrealized Mark-to-Market Loss	79		73
Total Loss on Commodity Derivative Instruments	72		96
Deferred Option Premium	18
Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	36			63
Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	44	[1]		7
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	13			21
Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	9			3
Crude Oil Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Realized Mark-to-Market (Gain) Loss	8		34
Total Unrealized Mark-to-Market Loss	41		92
Natural Gas Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Realized Mark-to-Market (Gain) Loss	(15)		(11)
Total Unrealized Mark-to-Market Loss	$ 38		$ (19)

[1] Includes $18 million of deferred put option premium.