Financial and Other Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	$ 1,955	$ 2,805
Derivative Liability Fair Value Gross Liability	(1,932)	(2,811)
Derivative Assets, Current	221	222
Derivative Assets, Noncurrent	75	74
Derivative Liabilities, Current	211	158
Derivative Liabilities, Noncurrent	62	89
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	1,585	2,272
Derivative Assets, Noncurrent	370	533
Derivative Liabilities, Current	(1,575)	(2,282)
Derivative Liabilities, Noncurrent	(357)	(529)
Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	1,585	2,272
Derivative Assets, Noncurrent	370	533
Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liabilities, Current	(1,575)	(2,282)
Derivative Liabilities, Noncurrent	(357)	(529)
Counterparty Netting [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	(1,364)	(2,050)
Derivative Assets, Noncurrent	(295)	(440)
Derivative Liabilities, Current	1,364	2,050
Derivative Liabilities, Noncurrent	295	440
Collateral Adjustment [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	0	0
Derivative Assets, Noncurrent	0	(19)
Derivative Liabilities, Current	0	74
Derivative Liabilities, Noncurrent	0	0
Derivative [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	221	222
Derivative Assets, Noncurrent	75	74
Derivative Liabilities, Current	(211)	(158)
Derivative Liabilities, Noncurrent	(62)	(89)
Designated as Hedging Instrument [Member] | Interest rate contracts [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	0	0
Derivative Liability Fair Value Gross Liability	(1)	(1)
Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	1,955	2,805
Derivative Liability Fair Value Gross Liability	(1,931)	(2,810)
Not Designated as Hedging Instrument [Member] | Foreign currency exchange contracts [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	1	3
Derivative Liability Fair Value Gross Liability	(1)	(5)
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	1,073	2,024
Derivative Liability Fair Value Gross Liability	(1,090)	(2,080)
Not Designated as Hedging Instrument [Member] | Electricity [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	819	747
Derivative Liability Fair Value Gross Liability	(796)	(705)
Not Designated as Hedging Instrument [Member] | Other Credit Derivatives [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	62	31
Derivative Liability Fair Value Gross Liability	$ (44)	$ (20)