Fair Value Measurements (Schedule Of Activity For Debt And Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Proceeds from sales and maturities of nuclear decommissioning trust investments	$ 249	$ 257	$ 1,043	$ 1,019
Gross realized gains on sales of securities held as available-for-sale	8	6	50	15
Gross realized losses on sales of securities held as available-for-sale	$ 0	$ 14	$ 8	$ 17