COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Connecticut Yankee Atomic Power Company [Abstract]
Percentage stock ownership in atomic power company (in hundredths)	9.50%
Carrying value of stock in atomic power company	$ 0.2
Regulatory asset related to atomic power company	15.8
Loss Contingencies [Line Items]
Ownership percentage in joint venture (in hundredths)	50.00%
Purchase and Sale Agreement [Abstract]
Sale price of Electric System Work Center (ESWC)	10.2
Original purchase price of ESWC	16.0
Positive Outcome of Litigation [Member]
DOE Spent Fuel Litigation [Abstract]
Damages awarded for spent fuel-related costs	39.7
Entity's share of amount awarded to atomic power company	3.8
Second set of damage claims relating to failure to remove spent atomic fuel	135.0
Entity's share of second set of damage claims	12.8
Mill River New Haven Connecticut Site [Member]
Site Contingency [Line Items]
Amount placed in escrow for estimated remediation	1.9
Amount of escrow fund unexpended	0.1
New Haven Harbor Station Site [Member]
Site Contingency [Line Items]
Site contingency, liability accrued	3.2
Pine Street Bridgeport Connecticut Site [Member]
Site Contingency [Line Items]
Site contingency, liability accrued	1.9
Minimum range of future remediation costs	2.0
Maximum range of future remediation costs	3.0
Chapel Street New Haven Connecticut Site [Member]
Site Contingency [Line Items]
Remediation costs incurred	1.2
Mill Street Greenfield Massachusetts Site [Member]
Site Contingency [Line Items]
Site contingency, liability accrued	5.0
Low range of threshold for future expenses	5.0
Middletown/Norwalk Transmission Project [Member]
Loss Contingencies [Line Items]
Amount sought for change order requests	34.5
GennConn Devon Facility [Member]
Loss Contingencies [Line Items]
Settlement amount paid	10.5
GennConn Middletown Facility [Member]
Loss Contingencies [Line Items]
Settlement amount paid	3.0
Guarantee Obligations [Member]
Loss Contingencies [Line Items]
Maximum amount of possible loss	$ 6.0