SEGMENT INFORMATION - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) segment
CL&P
Segment Reporting Information [Line Items]
Number of reportable segments	1
NSTAR Electric
Segment Reporting Information [Line Items]
Number of reportable segments	1
PSNH
Segment Reporting Information [Line Items]
Number of reportable segments	1
Affiliated Entity
Segment Reporting Information [Line Items]
Amount of natural gas transmission purchased | $	$ 62.5