COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details) $ in Millions		12 Months Ended
Jul. 15, 2016 USD ($) kV	Dec. 31, 2018 USD ($)
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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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