Financial and Other Derivative Instruments (Effect of Derivatives not Designated as Hedging Instruments on the Consolidated Statement of Operations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ 25	$ 101	$ (50)	$ 122
Foreign currency exchange contracts | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	0	3	1	(1)
Natural Gas | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	(4)	155	(130)	28
Natural Gas | Fuel, purchased power and gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	12	(9)	33	11
Electricity | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	15	(45)	46	88
Other | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives	$ 2	$ (3)	$ 0	$ (4)