Derivative Instruments And Hedging Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Schedule of Investments [Line Items]
Energy supply and hedging activities credit exposure total	$ 119
Makeup of net credit exposure, with investment-grade counterparties	45
Makeup of net credit exposure with commodity exchange brokers	38
Makeup of net credit exposure independent system operators	33
Makeup of net credit exposure non-rated counter parties	3
Number of contracts considered derivatives	1,328
Unrealized gain (loss) on derivatives	(126)	[1]	(138)	[1]
Interest Rate Swap [Member]
Schedule of Investments [Line Items]
Unrealized gain (loss) on derivatives	(8)
Derivative, fixed interest rate	6.09%
Increase in the fair value of derivative	$ 2

[1] Qualifying derivative contracts, which have been designated as normal purchases or normal sales contracts, are not reported at fair value under the accounting rules for derivatives and hedging and, therefore, are excluded from the table.