Financial Instruments (Table 4) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Operating Revenues [Member] | Production Related Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	$ 251	$ 184	$ 274	$ 468
Operating Revenues [Member] | Other Natural Gas and Power Derivatives Not Designated as Hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	(1)	(14)	(8)	(40)
Operating Revenues [Member] | Total [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	250	170	266	428
Interest Expense [Member] | Total Interest Rate Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	12	4	20	13
Interest Expense [Member] | Total [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	12	4	20	13
Other Comprehensive Income (Loss) [Member] | Production Related Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	2	2	8	8
Other Comprehensive Income (Loss) [Member] | Total Interest Rate Derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	84	(43)	53	(89)
Other Comprehensive Income (Loss) [Member] | Total [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net, Total	$ 86	$ (41)	$ 61	$ (81)