Risk Management and Fair Values (Schedules Of Valuation Techniques) (Details) $ in Millions	Mar. 31, 2019 USD ($)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	$ (46)
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	$ (6)
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	$ (5)