Fair Value Measurements (Schedule Of Activity For Debt And Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Proceeds from sales and maturities of nuclear decommissioning trust investments	$ 324	$ 282	$ 794	$ 721
Gross realized gains on sales of securities held as available-for-sale	13	4	42	9
Gross realized losses on sales of securities held as available-for-sale	$ 3	$ 1	$ 8	$ 3