Fair Value Measurements (Schedule Of Activity For Debt And Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Proceeds from sales and maturities of nuclear decommissioning trust investments	$ 257	$ 244	$ 1,019	$ 1,023
Gross realized gains on sales of securities held as available-for-sale	6	3	15	50
Gross realized losses on sales of securities held as available-for-sale	$ (14)	$ (12)	$ (17)	$ (25)