Derivative Financial Instruments Recorded in Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative, Fair Value, Net [Abstract]
Derivative Asset Not Designated As Hedging Instrument, Fair Value	$ 164	$ 37
Derivative Asset, Fair Value, Gross Liability	(60)	(11)
Derivative Liability Not Designated as Hedging Instrument Fair Value	(61)	(73)
Derivative Liability, Fair Value, Gross Asset	60	11
Derivative Asset, Current	48	0
Derivative Asset, Noncurrent	56	26
Derivative Liability, Current	1	62
Derivative Liability, Noncurrent	0	0
Natural gas contracts [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Asset Not Designated As Hedging Instrument, Fair Value	23	11
Derivative Asset, Fair Value, Gross Liability	(3)	(2)
Derivative Liability Not Designated as Hedging Instrument Fair Value	(4)	(22)
Derivative Liability, Fair Value, Gross Asset	3	2
Derivative Asset, Current	15	0
Derivative Asset, Noncurrent	5	9
Derivative Liability, Current	1	20
Derivative Liability, Noncurrent	0	0
Oil contracts [Member]
Derivative, Fair Value, Net [Abstract]
Derivative Asset Not Designated As Hedging Instrument, Fair Value	141	26
Derivative Asset, Fair Value, Gross Liability	(57)	(9)
Derivative Liability Not Designated as Hedging Instrument Fair Value	(57)	(51)
Derivative Liability, Fair Value, Gross Asset	57	9
Derivative Asset, Current	33	0
Derivative Asset, Noncurrent	51	17
Derivative Liability, Current	0	42
Derivative Liability, Noncurrent	$ 0	$ 0

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 within one year or 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, 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.

+ References+ Details

- Definition

Fair value, after the 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, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details

- Definition

Fair value, after the 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, 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.

+ References+ Details