COMMITMENTS AND CONTINGENCIES - Schedule of Number of Sites and Reserves (Details) - site	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Number of Sites	57	60
CL&P
Loss Contingencies [Line Items]
Number of Sites	15	15
NSTAR Electric
Loss Contingencies [Line Items]
Number of Sites	15	16
PSNH
Loss Contingencies [Line Items]
Number of Sites	9	9