ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
AOCI Cash Flow Hedging Component [Abstract]
Beginning Balance - Accumulated Other Comprehensive Income Loss Cumulative Changes In Net Gain Loss From Cash Flow Hedges Effect Net Of Tax	$ (16,400,000)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	500,000
Ending Balance - Accumulated Other Comprehensive Income Loss Cumulative Changes In Net Gain Loss From Cash Flow Hedges Effect Net Of Tax	(15,900,000)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	516,000	423,000
AOCI Unrealized GainLoss component [Abstract]
AOCI Unrealized Gains/Losses on Other Securities	1,300,000
OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax	(100,000)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(181,000)	34,000
AOCI Unrealized Gains/Losses on Other Securities-Ending Balance	1,200,000
AOCI Defined Benefit Component [Abstract]
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(57,800,000)
OtherComprehensiveIncomeReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostNetOfTax	1,600,000
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,621,000	1,407,000
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(56,200,000)
AOCI Rollforward [Abstract]
AOCI Beginning Balance	(72,854,000)
AmountReclassifiedFromAOCI	2,100,000
OtherComprehensiveIncomeBeforeReclassifications	(100,000)
Other Comprehensive Income (Loss), Net of Tax, Total	1,956,000	1,864,000
AOCI ending Balance	(70,898,000)
Reclassication of Items out of AOCI [Abstract]
OtherComprehensiveIncomeLossReclassificationAdjustmentOnDerivativesIncludedInNetIncomeBeforeTax	(800,000)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	(500,000)
OtherComprehensiveIncomeLossReclassificationAdjustmentOnDerivativesIncludedInNetIncomeTax	(300,000)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, before Tax	(2,600,000)
OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	(2,600,000)
OtherComprehensiveIncomeReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostNetOfTax	(1,600,000)
AmountReclassifiedFromAOCI	(2,100,000)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax	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
AOCI Unrealized GainLoss component [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(6,000)	1,000
AOCI Rollforward [Abstract]
AOCI Beginning Balance	(1,800,000)
Other Comprehensive Income (Loss), Net of Tax, Total	105,000	112,000
AOCI ending Balance	(1,695,000)
Public Service Company Of New Hampshire [Member]
AOCI Cash Flow Hedging Component [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	291,000	290,000
AOCI Unrealized GainLoss component [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(11,000)	2,000
AOCI Defined Benefit Component [Abstract]
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(3,000)
AOCI Rollforward [Abstract]
AOCI Beginning Balance	(9,655,000)
Other Comprehensive Income (Loss), Net of Tax, Total	277,000	292,000
AOCI ending Balance	(9,378,000)
Western Massachusetts Electric Company [Member]
AOCI Cash Flow Hedging Component [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	85,000	85,000
AOCI Unrealized GainLoss component [Abstract]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	(2,000)	0
AOCI Rollforward [Abstract]
AOCI Beginning Balance	(3,846,000)
Other Comprehensive Income (Loss), Net of Tax, Total	83,000	85,000
AOCI ending Balance	$ (3,763,000)