Fair Value Measurements (Schedule Of Activity For Debt And Equity Securities) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Proceeds from sales and maturities of nuclear decommissioning trust investments	$ 182	$ 357	$ 1,059	$ 1,152
Gross realized gains on sales of securities held as available-for-sale	30	7	114	44
Gross realized losses on sales of securities held as available-for-sale	$ 0	$ (4)	$ (3)	$ (10)