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EMPLOYEE BENEFITS - Schedule of Defined Contribution Plans (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, cost recognized $ 76.2 $ 67.3 $ 59.9
CL&P      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, cost recognized 10.6 9.0 7.7
NSTAR Electric      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, cost recognized 15.4 13.7 12.8
PSNH      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, cost recognized $ 6.0 $ 5.4 $ 4.8