ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			$ (74,009)	$ (46,000)
Other Comprehensive Income Before Reclassifications, Net of Tax			(1,500)	1,700
Reclassification From OCI, Net Of Tax			3,500	2,800
Other Comprehensive Income (Loss), Net of Tax, Total	$ 381	$ 2,814	1,976	4,524
AOCI Ending Balance	(72,033)	(41,500)	(72,033)	(41,500)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(92,259)	(92,495)	(187,102)	(182,471)
Income Tax Expense	(123,268)	(77,774)	(276,494)	(219,319)
Net Income Attributable to Controlling Interests	207,507	127,367	460,761	363,324
The Connecticut Light And Power Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(931)
Other Comprehensive Income (Loss), Net of Tax, Total	68	118	183	237
AOCI Ending Balance	(748)		(748)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(36,124)	(37,470)	(72,748)	(71,713)
Income Tax Expense	(43,129)	(20,401)	(81,276)	(65,942)
Public Service Company Of New Hampshire [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(7,369)
Other Comprehensive Income (Loss), Net of Tax, Total	215	303	514	607
AOCI Ending Balance	(6,855)		(6,855)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(11,662)	(10,999)	(22,935)	(22,971)
Income Tax Expense	(15,701)	(14,897)	(35,977)	(34,597)
Western Massachusetts Electric Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(3,176)
Other Comprehensive Income (Loss), Net of Tax, Total	72	86	158	173
AOCI Ending Balance	(3,018)		(3,018)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(6,291)	(6,707)	(13,112)	(12,353)
Income Tax Expense	(9,693)	(4,548)	(18,807)	(16,106)
Qualified Cash Flow Hedging Instruments [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(12,400)	(14,400)
Reclassification From OCI, Net Of Tax			1,000	1,000
Other Comprehensive Income (Loss), Net of Tax, Total			1,000	1,000
AOCI Ending Balance	(11,400)	(13,400)	(11,400)	(13,400)
Unrealized Gains Losses on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			700	400
Other Comprehensive Income Before Reclassifications, Net of Tax			(1,100)	500
Other Comprehensive Income (Loss), Net of Tax, Total			(1,100)	500
AOCI Ending Balance	(400)	900	(400)	900
Pension, SERP and PBOP Benefit Plans [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(62,300)	(32,000)
Other Comprehensive Income Before Reclassifications, Net of Tax			(400)	1,200
Reclassification From OCI, Net Of Tax			2,500	1,800
Other Comprehensive Income (Loss), Net of Tax, Total			2,100	3,000
AOCI Ending Balance	$ (60,200)	$ (29,000)	$ (60,200)	$ (29,000)