Nuclear Decommissioning Trust Fund Investments (Costs And Fair Values Of Investments In Debt Securities In Nuclear Decommissioning Trust Fund According To Contractual Maturities) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Investments, Debt and Equity Securities [Abstract]
Cost, Less than 5 years	$ 105
Cost, 5 years to 10 years	47
Cost, Due after 10 years	45
Cost, Total	197
Fair Value, Less than 5 years	104
Fair Value, 5 years to 10 years	47
Fair Value, Due after 10 years	45
Fair Value, Total	$ 196