Derivative and Hedging Activities - Derivative Instruments in Balance Sheet Table (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 469	$ 652
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	469	652
Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	254	721
Not Designated as Hedging Instrument [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	254	722
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	254	722
Not Designated as Hedging Instrument [Member] \| Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		(17)
Derivative Liability, Fair Value, Gross Asset		0
Derivative, Fair Value, Net		(17)
Not Designated as Hedging Instrument [Member] \| Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	291
Derivative Liability, Fair Value, Gross Asset	0
Derivative, Fair Value, Net	291
Not Designated as Hedging Instrument [Member] \| Other Current Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	370	974
Derivative Asset, Fair Value, Gross Liability	(71)	(95)
Derivative, Fair Value, Net	299	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	43
Derivative Asset, Fair Value, Gross Liability	0
Derivative, Fair Value, Net	43
Not Designated as Hedging Instrument [Member] \| Other Noncurrent Assets [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	12	16
Derivative Asset, Fair Value, Gross Liability	(3)	(10)
Derivative, Fair Value, Net	9	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	248
Derivative Asset, Fair Value, Gross Liability	0
Derivative, Fair Value, Net	248
Not Designated as Hedging Instrument [Member] \| Other Current Liabilities [Member] \| Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	(95)	(105)
Derivative Liability, Fair Value, Gross Asset	71	95
Derivative, Fair Value, Net	(24)	(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		(5)
Derivative Liability, Fair Value, Gross Asset		0
Derivative, Fair Value, Net		(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	(33)	(163)
Derivative Liability, Fair Value, Gross Asset	3	10
Derivative, Fair Value, Net	(30)	(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	(76)	(53)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	(76)	(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	(76)	(53)
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative, Fair Value, Net	$ (76)	$ (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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