Financial and Other Derivative Instruments (Effect of Derivatives not Deisgnated as Hedging Instruments on the Consolidated Statement of Operations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives for Years Ended December 31,	$ (28)	$ 79
Foreign currency exchange contracts | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives for Years Ended December 31,	3	(2)
Natural Gas | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives for Years Ended December 31,	(34)	(30)
Natural Gas | Fuel, purchased power and gas
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives for Years Ended December 31,	(44)	(5)
Electricity | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives for Years Ended December 31,	54	123
Other | Operating Revenue
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on Derivatives for Years Ended December 31,	$ (7)	$ (7)