Financial and Other Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	$ 1,444	$ 2,805
Derivative Liability Fair Value Gross Liability	(1,435)	(2,811)
Derivative Assets, Current	123	222
Derivative Assets, Noncurrent	63	74
Derivative Liabilities, Current	146	158
Derivative Liabilities, Noncurrent	30	89
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	1,161	2,272
Derivative Assets, Noncurrent	283	533
Derivative Liabilities, Current	(1,185)	(2,282)
Derivative Liabilities, Noncurrent	(250)	(529)
Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	1,161	2,272
Derivative Assets, Noncurrent	283	533
Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liabilities, Current	(1,185)	(2,282)
Derivative Liabilities, Noncurrent	(250)	(529)
Counterparty Netting [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	(1,038)	(2,050)
Derivative Assets, Noncurrent	(220)	(440)
Derivative Liabilities, Current	1,038	2,050
Derivative Liabilities, Noncurrent	220	440
Collateral Adjustment [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	0	0
Derivative Assets, Noncurrent	0	(19)
Derivative Liabilities, Current	1	74
Derivative Liabilities, Noncurrent	0	0
Derivative [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	123	222
Derivative Assets, Noncurrent	63	74
Derivative Liabilities, Current	(146)	(158)
Derivative Liabilities, Noncurrent	(30)	(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	1,444	2,805
Derivative Liability Fair Value Gross Liability	(1,434)	(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	(2)	(5)
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	959	2,024
Derivative Liability Fair Value Gross Liability	(975)	(2,080)
Not Designated as Hedging Instrument [Member] | Electricity [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	431	747
Derivative Liability Fair Value Gross Liability	(419)	(705)
Not Designated as Hedging Instrument [Member] | Other Credit Derivatives [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	53	31
Derivative Liability Fair Value Gross Liability	$ (38)	$ (20)