Derivative Instruments And Hedging Activities (Number Of Derivative Contracts By Commodity Type) (Details)	3 Months Ended
	Mar. 31, 2012
Electric Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Contracts	754	[1]
MWhs	16,197,114	[2]
Number of Capacity Contracts	59	[1]
MWs	7,639	[2]
Gas Derivatives [Member]
Derivatives, Fair Value [Line Items]
Number of Contracts	579	[1]
Number of Capacity Contracts	1,392	[1]
Dths	91,840,940	[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.

[2] Volumes are reported net of long and short positions.