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PROPERTY, PLANT AND EQUIPMENT AND ACCUMULATED DEPRECIATION - Schedule of Aggregate Composite Depreciation Rates (Details)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Property, Plant and Equipment [Line Items]      
Composite depreciation rate for plant in service (in percent) 3.20% 3.10% 3.00%
CL&P      
Property, Plant and Equipment [Line Items]      
Composite depreciation rate for plant in service (in percent) 2.90% 2.80% 2.80%
NSTAR Electric      
Property, Plant and Equipment [Line Items]      
Composite depreciation rate for plant in service (in percent) 2.80% 2.70% 2.70%
PSNH      
Property, Plant and Equipment [Line Items]      
Composite depreciation rate for plant in service (in percent) 3.00% 3.00% 3.00%