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SEGMENT INFORMATION - Narrative (Details)
$ in Millions
6 Months Ended
Jun. 30, 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