EMPLOYEE BENEFITS - Schedule of Compensation Expense and Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	$ 27.8	$ 33.4	$ 28.2
Future Income Tax Benefit	7.3	8.7	7.3
CL&P
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	8.7	10.0	8.8
Future Income Tax Benefit	2.3	2.6	2.3
NSTAR Electric
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	8.7	10.7	9.0
Future Income Tax Benefit	2.3	2.8	2.3
PSNH
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	3.0	3.6	3.0
Future Income Tax Benefit	$ 0.8	$ 0.9	$ 0.8