Financial and Other Derivative Instruments (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	$ 109	$ 131
Derivative Assets, Noncurrent	59	77
Derivative Liabilities, Current	114	142
Derivative Liabilities, Noncurrent	62	110
Total derivatives:
Assets, Current	2,911	3,167
Assets, Noncurrent	7,027	7,280
Liabilities, Current	2,100	2,749
Liabilities, Noncurrent	8,174	8,291
Designated as Hedging Instrument [Member] | Interest Rate Contract [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 Contract [Member] | Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	0
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liability Fair Value Gross Liability	(1)
Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	2,174	2,848
Derivative Liability Fair Value Gross Liability	(2,185)	(2,936)
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract Member
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset		20
Derivative Liability Fair Value Gross Liability		(30)
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract Member | Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	6
Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract Member | Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liability Fair Value Gross Liability	(9)
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset		1,986
Derivative Liability Fair Value Gross Liability		(2,118)
Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	1,746
Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liability Fair Value Gross Liability	(1,795)
Not Designated as Hedging Instrument [Member] | Electricity [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset		766
Derivative Liability Fair Value Gross Liability		(716)
Not Designated as Hedging Instrument [Member] | Electricity [Member] | Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	393
Not Designated as Hedging Instrument [Member] | Electricity [Member] | Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liability Fair Value Gross Liability	(365)
Not Designated as Hedging Instrument [Member] | Other [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset		76
Derivative Liability Fair Value Gross Liability		(71)
Not Designated as Hedging Instrument [Member] | Other [Member] | Derivative Asset [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	29
Not Designated as Hedging Instrument [Member] | Other [Member] | Derivative Liabilities [Member]
Derivatives designated as hedging instruments:
Derivative Liability Fair Value Gross Liability	(15)
Not Designated as Hedging Instrument [Member] | Total [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	2,174	2,848
Derivative Liability Fair Value Gross Liability	(2,184)	(2,935)
Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	109	131
Derivative Assets, Noncurrent	59	77
Derivative Liabilities, Current	(114)	(142)
Derivative Liabilities, Noncurrent	(62)	(110)
Derivative Asset [Member]
Total derivatives:
Assets, Current	1,635	2,011
Assets, Noncurrent	539	837
Derivative Liabilities [Member]
Total derivatives:
Liabilities, Current	(1,643)	(2,041)
Liabilities, Noncurrent	(542)	(895)
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	1,635	2,011
Derivative Assets, Noncurrent	539	837
Derivative Liabilities, Current	(1,643)	(2,041)
Derivative Liabilities, Noncurrent	(542)	(895)
Counterparty Netting [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	(1,526)	(1,871)
Derivative Assets, Noncurrent	(480)	(760)
Derivative Liabilities, Current	1,526	1,871
Derivative Liabilities, Noncurrent	480	760
Collateral Adjustment [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets, Current	0	(9)
Derivative Assets, Noncurrent	0	0
Derivative Liabilities, Current	3	28
Derivative Liabilities, Noncurrent	$ 0	$ 25