ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
AOCI Cash Flow Hedging Component [Abstract]
Beginning Balance -AOCI From CF Hedges Effect Net Of Tax			$ (16,400,000)
OCI Amortization of Cash Flow Hedge, Net of Tax	500,000		1,500,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(509,000)	(516,000)	(1,539,000)	(1,455,000)
Ending Balance - AOCI From CFHedges Effect Net Of Tax	(14,900,000)		(14,900,000)
AOCI Unrealized GainLoss component [Abstract]
AOCI Unrealized Gains/Losses on Other Securities			1,300,000
OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax			(800,000)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(38,000)	217,000	(810,000)	411,000
AOCI Unrealized Gains/Losses on Other Securities-Ending Balance	500,000		500,000
AOCI Defined Benefit Component [Abstract]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax			(57,800,000)
OCI Reclassification Of Defined Benefit Plans Net Gain Loss Net of Tax	1,600,000		4,800,000
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,611,000	1,445,000	4,738,000	4,611,000
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(53,000,000)		(53,000,000)
AOCI Rollforward [Abstract]
AOCI Beginning Balance			(72,854,000)
AmountReclassifiedFromAOCI	2,100,000		6,300,000
OtherComprehensiveIncomeBeforeReclassifications			(800,000)
Other Comprehensive Income (Loss), Net of Tax, Total	2,082,000	2,178,000	5,467,000	6,477,000
AOCI ending Balance	(67,387,000)		(67,387,000)
Reclassication of Items out of AOCI [Abstract]
OCI Amortization of Cash Flow Hedges, Before Tax	(800,000)		(2,500,000)
OCI Amortization of Cash Flow Hedge, Net of Tax	(500,000)		(1,500,000)
OCI Amortization of Prior Service Cost			(100,000)
OCI Reclass, Defined Benefit, Net GainLoss before Tax	(2,500,000)		(7,300,000)
OCI Defined Benefit Plan Tax	900,000		2,600,000
OCI Reclassification Of Defined Benefit Plans Net Gain Loss Net of Tax	(1,600,000)		(4,800,000)
AmountReclassifiedFromAOCI	(2,100,000)		(6,300,000)
OCI Reclass CF Hedging Tax	300,000		1,000,000
The Connecticut Light And Power Company [Member]
AOCI Cash Flow Hedging Component [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(111,000)	(111,000)	(333,000)	(333,000)
AOCI Unrealized GainLoss component [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(1,000)	8,000	(27,000)	14,000
AOCI Rollforward [Abstract]
AOCI Beginning Balance			(1,800,000)
Other Comprehensive Income (Loss), Net of Tax, Total	110,000	119,000	306,000	347,000
AOCI ending Balance	(1,494,000)		(1,494,000)
Public Service Company Of New Hampshire [Member]
AOCI Cash Flow Hedging Component [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(290,000)	(291,000)	(872,000)	(872,000)
AOCI Unrealized GainLoss component [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2,000)	13,000	(47,000)	24,000
AOCI Defined Benefit Component [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	0	(2,000)	(3,000)	2,000
AOCI Rollforward [Abstract]
AOCI Beginning Balance			(9,655,000)
Other Comprehensive Income (Loss), Net of Tax, Total	288,000	302,000	822,000	898,000
AOCI ending Balance	(8,833,000)		(8,833,000)
Western Massachusetts Electric Company [Member]
AOCI Cash Flow Hedging Component [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(85,000)	(84,000)	(254,000)	(253,000)
AOCI Unrealized GainLoss component [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	0	2,000	(8,000)	4,000
AOCI Rollforward [Abstract]
AOCI Beginning Balance			(3,846,000)
Other Comprehensive Income (Loss), Net of Tax, Total	85,000	86,000	246,000	257,000
AOCI ending Balance	$ (3,600,000)		$ (3,600,000)