ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			$ (46,031,000)	$ (72,900,000)
Other Comprehensive Income Before Reclassifications, Net of Tax			1,400,000	(800,000)
Reclassification From OCI, Net Of Tax			4,400,000	6,300,000
Other Comprehensive Income (Loss), Net of Tax, Total	1,335,000	2,082,000	5,859,000	5,467,000
AOCI Ending Balance	(40,172,000)	(67,400,000)	(40,172,000)	(67,400,000)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(89,738,000)	(87,476,000)	(272,208,000)	(250,583,000)
Income Tax Expense	(126,539,000)	(109,351,000)	(345,858,000)	(325,442,000)
Net Income Attributable to Controlling Interests	234,614,000	209,501,000	597,937,000	608,610,000
The Connecticut Light And Power Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(1,387,000)
Other Comprehensive Income (Loss), Net of Tax, Total	104,000	110,000	341,000	306,000
AOCI Ending Balance	(1,046,000)		(1,046,000)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(38,735,000)	(35,284,000)	(110,448,000)	(98,964,000)
Income Tax Expense	(30,038,000)	(36,136,000)	(95,980,000)	(113,149,000)
Public Service Company Of New Hampshire [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(8,550,000)
Other Comprehensive Income (Loss), Net of Tax, Total	277,000	288,000	885,000	822,000
AOCI Ending Balance	(7,665,000)		(7,665,000)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(11,024,000)	(10,866,000)	(33,995,000)	(34,181,000)
Income Tax Expense	(17,603,000)	(18,196,000)	(52,199,000)	(52,797,000)
Western Massachusetts Electric Company [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(3,517,000)
Other Comprehensive Income (Loss), Net of Tax, Total	83,000	85,000	256,000	246,000
AOCI Ending Balance	(3,261,000)		(3,261,000)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(6,576,000)	(6,231,000)	(18,929,000)	(18,800,000)
Income Tax Expense	(10,490,000)	(8,588,000)	(26,596,000)	(30,424,000)
Qualified Cash Flow Hedging Instruments [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(14,400,000)	(16,400,000)
Reclassification From OCI, Net Of Tax			1,500,000	1,500,000
Other Comprehensive Income (Loss), Net of Tax, Total			1,500,000	1,500,000
AOCI Ending Balance	(12,900,000)	(14,900,000)	(12,900,000)	(14,900,000)
Unrealized Gains Losses on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			400,000	1,300,000
Other Comprehensive Income Before Reclassifications, Net of Tax			200,000	(800,000)
Other Comprehensive Income (Loss), Net of Tax, Total			200,000	(800,000)
AOCI Ending Balance	600,000	500,000	600,000	500,000
Pension, SERP and PBOP Benefit Plans [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax RollForward [Abstract]
AOCI Beginning Balance			(32,000,000)	(57,800,000)
Other Comprehensive Income Before Reclassifications, Net of Tax			1,200,000
Reclassification From OCI, Net Of Tax			2,900,000	4,800,000
Other Comprehensive Income (Loss), Net of Tax, Total			4,100,000	4,800,000
AOCI Ending Balance	(27,900,000)	(53,000,000)	(27,900,000)	(53,000,000)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Net Income Attributable to Controlling Interests	(1,500,000)	(2,100,000)	(4,400,000)	(6,300,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Qualified Cash Flow Hedging Instruments [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
Total Interest Expense	(800,000)	(800,000)	(2,500,000)	(2,500,000)
Income Tax Expense	300,000	300,000	1,000,000	1,000,000
Net Income Attributable to Controlling Interests	(500,000)	(500,000)	(1,500,000)	(1,500,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension, SERP and PBOP Benefit Plans [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Abstract]
OCI Reclassification Adjustment for Net Actuarial Gain (Loss), before Tax	(1,600,000)	(2,500,000)	(4,700,000)	(7,300,000)
OCI Reclassification Adjustment for Amortization of Prior Service Cost, before tax	0	0	(100,000)	(100,000)
OCI Reclassification Adjustment for Pension, SERP and PBOP Plans, before Tax	(1,600,000)	(2,500,000)	(4,800,000)	(7,400,000)
Income Tax Expense	600,000	900,000	1,900,000	2,600,000
Net Income Attributable to Controlling Interests	$ (1,000,000)	$ (1,600,000)	$ (2,900,000)	$ (4,800,000)