Derivative and Hedging Activities - Derivative Instruments in Balance Sheet Table (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 395	$ 652
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	395	652
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	500	721
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	501	722
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	501	722
Not Designated as Hedging Instrument [Member] \| Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(3)	(17)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	(3)	(17)
Not Designated as Hedging Instrument [Member] \| Other Current Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	688	974
Derivative Asset, Fair Value, Gross Liability	(76)	(95)
Derivative, Fair Value, Net	612	879
Not Designated as Hedging Instrument [Member] \| Other Noncurrent Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		16
Derivative Asset, Fair Value, Gross Liability		(10)
Derivative, Fair Value, Net		6
Not Designated as Hedging Instrument [Member] \| Other Current Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(99)	(105)
Derivative Liability, Fair Value, Gross Asset	76	95
Derivative, Fair Value, Net	(23)	(10)
Not Designated as Hedging Instrument [Member] \| Other Current Liabilities [Member] \| Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(3)	(5)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	(3)	(5)
Not Designated as Hedging Instrument [Member] \| Other Noncurrent Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(88)	(163)
Derivative Liability, Fair Value, Gross Asset	0	10
Derivative, Fair Value, Net	(88)	(153)
Not Designated as Hedging Instrument [Member] \| Other Noncurrent Liabilities [Member] \| Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		(12)
Derivative Liability, Fair Value, Gross Asset		0
Derivative, Fair Value, Net		(12)
Designated as Hedging Instrument [Member] \| Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(103)	(53)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	(103)	(53)
Designated as Hedging Instrument [Member] \| Other Noncurrent Liabilities [Member] \| Foreign Exchange Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(103)	(53)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	$ (103)	$ (53)

Fair value, before 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 elected not to be offset. Excludes assets not subject to a master netting arrangement.

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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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