EMPLOYEE BENEFITS - Schedule of Funded Status (Details) - Pension and SERP - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 4,936.8	$ 4,911.6
CL&P
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	977.8	960.7
NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,051.9	1,055.1
PSNH
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 522.1	$ 516.9