Fair Value Measurements (Schedule Of Activity For Debt And Equity Securities) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Proceeds from sales and maturities of nuclear decommissioning trust investments	$ 347	$ 432	$ 877	$ 795
Gross realized gains on sales of securities held as available-for-sale	28	25	84	37
Gross realized losses on sales of securities held as available-for-sale	$ (2)	$ (5)	$ (3)	$ (6)