Risk Management and Fair Values (Schedules Of Valuation Techniques) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Minimum [Member]
Range from Average Percentage for Fair Value of Electricity Swaps	4.00%
Effect of Significant Unobservable Inputs on Fair Value of Electricity Swaps	$ 6
Maximum [Member]
Range from Average Percentage for Fair Value of Electricity Swaps	4.75%
Effect of Significant Unobservable Inputs on Fair Value of Electricity Swaps	$ 7
Electricity Futures Forwards Swaps And Options [Member]
Fair Value of Electricity Swaps - Net Liability Position	$ (65)