Derivative and Hedging Activities - Derivative Instruments in Balance Sheet Table (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 391	$ 652
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	391	652
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	258	721
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	258	722
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	258	722
Not Designated as Hedging Instrument [Member] \| Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	(17)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	0	(17)
Not Designated as Hedging Instrument [Member] \| Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	221
Derivative Liability, Fair Value, Gross Asset	0
Derivative, Fair Value, Net	221
Not Designated as Hedging Instrument [Member] \| Other Current Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	426	974
Derivative Asset, Fair Value, Gross Liability	(74)	(95)
Derivative, Fair Value, Net	352	879
Not Designated as Hedging Instrument [Member] \| Other Current Assets [Member] \| Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	35
Derivative Asset, Fair Value, Gross Liability	0
Derivative, Fair Value, Net	35
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 Noncurrent Assets [Member] \| Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	186
Derivative, Fair Value, Net	186
Not Designated as Hedging Instrument [Member] \| Other Current Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(101)	(105)
Derivative Liability, Fair Value, Gross Asset	74	95
Derivative, Fair Value, Net	(27)	(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	0	(5)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	0	(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	(67)	(163)
Derivative Liability, Fair Value, Gross Asset	0	10
Derivative, Fair Value, Net	(67)	(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	(88)	(53)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	(88)	(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	(88)	(53)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	$ (88)	$ (53)

Fair value of liability associated with 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.

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