Derivative Instruments And Hedging Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011
Schedule of Investments [Line Items]
Energy supply and hedging activities credit exposure total	$ 120
Makeup of net credit exposure counterparties	60
Makeup of net credit exposure primarily with commodity exchange	44
Independent system operators	15
Number of contracts considered derivatives	1,565
Unrealized gain (loss) on derivatives	(9)
Derivative, fixed interest rate	6.09%
Non-Investment Grade Counterparties [Member]
Schedule of Investments [Line Items]
Makeup of net credit exposure primarily with commodity exchange	$ 1