Fair Value Measurements Level 3 Table and Phantom (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Crude Oil [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unobservable Input	Oil price volatility curves
Weighted average of price volatility curve, percentage	16.44%
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ (369)
Crude Oil [Member] | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Volatility Curve	9.94%
Crude Oil [Member] | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Volatility Curve	25.79%
Crude Oil [Member] | Basis Swap [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unobservable Input	Physical pricing point forward curves
Weighted Average Of Price Forward Curve	$ 4.33
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	1
Crude Oil [Member] | Basis Swap [Member] | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Forward Curve	3.03
Crude Oil [Member] | Basis Swap [Member] | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Forward Curve	4.65
Natural Gas [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unobservable Input	Natural gas price volatility curves
Weighted average of price volatility curve, percentage	22.10%
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	(215)
Natural Gas [Member] | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Volatility Curve	20.08%
Natural Gas [Member] | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Volatility Curve	34.86%
Natural Gas [Member] | Basis Swap [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unobservable Input	Physical pricing point forward curves
Weighted Average Of Price Forward Curve	$ (0.36)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ (2)
Natural Gas [Member] | Basis Swap [Member] | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Forward Curve	(1.64)
Natural Gas [Member] | Basis Swap [Member] | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Price Forward Curve	0.00