Derivative Instruments And Hedging Activities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Schedule of Investments [Line Items]
Energy supply and hedging activities credit exposure total	$ 121
Makeup of net credit exposure, with investment-grade counterparties	46
Makeup of net credit exposure with commodity exchange brokers	37
Makeup of net credit exposure independent system operators	36
Makeup of net credit exposure non-rated counterparties	2
Number of contracts, considered derivatives	1,392
Unrealized gain (loss) on derivatives	(90)	[1]	(17)	[1]
Interest Rate Swaps [Member]
Schedule of Investments [Line Items]
Unrealized gain (loss) on derivatives	$ (8)
Derivative, fixed interest rate	6.09%

[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.