Financial and Other Derivative Instruments (Fair Value of Derivative Instruments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	$ 926	$ 833
Derivative Liability Fair Value Gross Liability	(984)	(936)
Derivative Assets, Current	79	99
Derivative Assets, Noncurrent	17	27
Derivative Liabilities, Current	(140)	(195)
Derivative Liabilities, Noncurrent	(16)	(43)
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	841	691
Derivative Assets, Noncurrent	85	142
Derivative Liabilities, Current	(899)	(773)
Derivative Liabilities, Noncurrent	(85)	(163)
Natural Gas Commodity Contract [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	383	396
Derivative Liability Fair Value Gross Liability	(416)	(503)
Electricity Commodity Contract [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	503	400
Derivative Liability Fair Value Gross Liability	(524)	(398)
Other [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	40	37
Derivative Liability Fair Value Gross Liability	(40)	(34)
Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	926	833
Derivative Liability Fair Value Gross Liability	(984)	(936)
Not Designated as Hedging Instrument [Member] \| Foreign currency exchange contracts [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	0	0
Derivative Liability Fair Value Gross Liability	(4)	(1)
Not Designated as Hedging Instrument [Member] \| Natural Gas Commodity Contract [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	383	396
Derivative Liability Fair Value Gross Liability	(416)	(503)
Not Designated as Hedging Instrument [Member] \| Electricity Commodity Contract [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	503	400
Derivative Liability Fair Value Gross Liability	(524)	(398)
Not Designated as Hedging Instrument [Member] \| Other [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	40	37
Derivative Liability Fair Value Gross Liability	$ (40)	$ (34)

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.

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- 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