PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	3.30%	3.20%	3.10%
CL&P
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	2.90%	2.90%	2.80%
NSTAR Electric
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	2.80%	2.80%	2.70%
PSNH
Property, Plant and Equipment [Line Items]
Composite depreciation rate for plant in service (in percent)	3.00%	3.00%	3.00%