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Period Type:	duration

COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details) $ in Millions		12 Months Ended
	Jul. 15, 2016 kV	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Amount of capacity required for installation of distribution cable (in kV) \| kV	115
NSTAR Electric
Loss Contingencies [Line Items]
Base rate credit for new cable \| $		$ 17.5	$ 17.5