PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Average Remaining Useful Lives of Depreciable Assets (Details)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Distribution - Electric	34 years 3 months 18 days
Distribution - Natural Gas	43 years 2 months 12 days
Transmission - Electric	40 years 4 months 24 days
Distribution - Water	33 years 6 months
Solar	24 years 2 months 12 days
Other	11 years 2 months 12 days
Computer Software, Hardware and Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	5 years
Computer Software, Hardware and Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	15 years
Buildings
Property, Plant and Equipment [Line Items]
Estimated useful life of property, plant and equipment	40 years
CL&P
Property, Plant and Equipment [Line Items]
Distribution - Electric	35 years 3 months 18 days
Transmission - Electric	36 years 9 months 18 days
NSTAR Electric
Property, Plant and Equipment [Line Items]
Distribution - Electric	33 years 8 months 12 days
Transmission - Electric	44 years 10 months 24 days
Solar	24 years 2 months 12 days
PSNH
Property, Plant and Equipment [Line Items]
Distribution - Electric	33 years 2 months 12 days
Transmission - Electric	42 years 1 month 6 days