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Fair Value Measurements (Schedule Of Activity For Debt And Equity Securities) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Fair Value Measurements [Abstract]    
Proceeds from sales and maturities of nuclear decommissioning trust investments $ 351 $ 726
Gross realized gains on sales of securities held as available-for-sale 7 20
Gross realized losses on sales of securities held as available-for-sale $ (3) $ (4)