Derivative Instruments and Hedging Activities (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Commodity Derivative Assets, Current	$ 710us-gaap_DerivativeAssetsCurrent	$ 1us-gaap_DerivativeAssetsCurrent
Commodity Derivative Assets, Noncurrent	180us-gaap_DerivativeAssetsNoncurrent	16us-gaap_DerivativeAssetsNoncurrent
Derivative Asset	890us-gaap_DerivativeAssets	17us-gaap_DerivativeAssets
Liability Derivative Instruments	0	75
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(976)	133	(75)
Total Cash (Received) Paid in settlement of Commodity Derivative Instrument	(29)us-gaap_GainLossOnSaleOfDerivatives	2us-gaap_GainLossOnSaleOfDerivatives	34us-gaap_GainLossOnSaleOfDerivatives
Total Non-cash Portion of (Gain) Loss on Commodity Derivative Instruments	(947)	131	(109)
Crude Oil [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(897)	139	(37)
Total Cash (Received) Paid in settlement of Commodity Derivative Instrument	(34)	52	83
Total Non-cash Portion of (Gain) Loss on Commodity Derivative Instruments	(863)	87	(120)
Natural Gas [Member]
Derivatives, Fair Value [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	(79)	(6)	(38)
Total Cash (Received) Paid in settlement of Commodity Derivative Instrument	5	(50)	(49)
Total Non-cash Portion of (Gain) Loss on Commodity Derivative Instruments		44	11
Current Assets
Derivatives, Fair Value [Line Items]
Commodity Derivative Assets, Current	710	1
Current Liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Instruments	0	65
Noncurrent Assets
Derivatives, Fair Value [Line Items]
Commodity Derivative Assets, Noncurrent	180	16
Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Liability Derivative Instruments	$ 0	$ 10

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open derivatives, commodity, or energy contracts, held at each balance sheet date, that was included in earnings for the period.

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