Fair Value Measurements (Schedule Of Activity For Debt And Equity Securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurements [Abstract]
Proceeds from sales and maturities of nuclear decommissioning trust investments	$ 1,268	$ 1,336	$ 1,619
Gross realized gains on sales of securities held as available-for-sale	55	118	94
Gross realized losses on sales of securities held as available-for-sale	$ (37)	$ (12)	$ (13)