PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	3.10%	3.00%	3.10%
CL&P
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	2.80%	2.80%	2.80%
NSTAR Electric
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	2.70%	2.70%	2.80%
PSNH
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	3.00%	3.00%	3.10%