Risk Management and Fair Values (Schedules Of Valuation Techniques) (Details) $ in Millions	Jun. 30, 2018 USD ($)
Effect of Significant Unobservable Inputs on Fair Value of Electricity Swaps	$ (3)
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ (25)
Maximum [Member]
Range from Average Percentage for Fair Value of Electricity Swaps	4.75%
Minimum [Member]
Range from Average Percentage for Fair Value of Electricity Swaps	4.00%