Financial and Other Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	$ 2,805	$ 2,848
Derivative Liability Fair Value Gross Liability	(2,811)	(2,936)
Derivative Assets, Current	222	131
Derivative Assets, Noncurrent	74	77
Derivative Liabilities, Current	158	142
Derivative Liabilities, Noncurrent	89	110
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	2,272	2,011
Derivative Assets, Noncurrent	533	837
Derivative Liabilities, Current	(2,282)	(2,041)
Derivative Liabilities, Noncurrent	(529)	(895)
Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	2,272	2,011
Derivative Assets, Noncurrent	533	837
Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liabilities, Current	(2,282)	(2,041)
Derivative Liabilities, Noncurrent	(529)	(895)
Counterparty Netting [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	(2,050)	(1,871)
Derivative Assets, Noncurrent	(440)	(760)
Derivative Liabilities, Current	2,050	1,871
Derivative Liabilities, Noncurrent	440	760
Collateral Adjustment [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	0	(9)
Derivative Assets, Noncurrent	(19)	0
Derivative Liabilities, Current	74	28
Derivative Liabilities, Noncurrent	0	25
Derivative [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	222	131
Derivative Assets, Noncurrent	74	77
Derivative Liabilities, Current	(158)	(142)
Derivative Liabilities, Noncurrent	(89)	(110)
Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset		0
Derivative Liability Fair Value Gross Liability		(1)
Designated as Hedging Instrument [Member] | Interest rate contracts [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	0
Derivative Liability Fair Value Gross Liability	(1)
Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	2,805	2,848
Derivative Liability Fair Value Gross Liability	(2,810)	(2,935)
Not Designated as Hedging Instrument [Member] | Foreign currency exchange contracts [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	3	20
Derivative Liability Fair Value Gross Liability	(5)	(30)
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	2,024	1,986
Derivative Liability Fair Value Gross Liability	(2,080)	(2,118)
Not Designated as Hedging Instrument [Member] | Electricity [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	747	766
Derivative Liability Fair Value Gross Liability	(705)	(716)
Not Designated as Hedging Instrument [Member] | Other [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	31	76
Derivative Liability Fair Value Gross Liability	$ (20)	$ (71)