COMMITMENTS AND CONTINGENCIES - Eversource and NSTAR Electric Boston Harbor Civil Action (Details)	12 Months Ended
Dec. 31, 2016 kV
Commitments and Contingencies Disclosure [Abstract]
Amount of capacity required for installation of distribution cable (in kV)	115

Capacity Required For Installation of Distribution Cable

No definition available.

Name:	es_CapacityRequiredForInstallationOfDistributionCable
Namespace Prefix:	es_
Data Type:	dtr-types:voltageItemType
Balance Type:	na
Period Type:	duration