COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
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
Entity's share of second set of damage claims	12.8
Middletown/Norwalk transmission project [Abstract]
Amount sought for change order requests	33.3
Revised amount sought for change order requests	8.4
Percentage of general contractor mark-up on approved subcontractor change order claims (in hundredths)	10.00%
Amount of general contractor mark up on approved subcontractor change order claims	2.3
Purchase and sales agreement [Abstract]
Sales price of Electric System Work Center (ESWC)	10.2
Original purchase price of ESWC	16
Connecticut Yankee Atomic Power Company [Member]
Site Contingency [Line Items]
Percentage stock ownership share 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	12.7
Mill River New Haven Connecticut Site [Member]
Middletown/Norwalk transmission project [Abstract]
Amount sought for change order requests	1.9
Revised amount sought for change order requests	0.1
New Haven Harbor Station Site [Member]
Site Contingency [Line Items]
Site contingency, liability accrued	3.2
Mill Street Greenfield Massachusetts Site [Member]
Site Contingency [Line Items]
Site contingency, liability accrued	5.8
Low range of threshold for future expenses	5.8
East Street Site Pittsfield Massachusetts [Member]
Site Contingency [Line Items]
Site contingency, liability accrued	2.7
Amount demanded as share of response costs	$ 0.7