EMPLOYEE BENEFITS - Schedule of Compensation Expense and Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	$ 28.2	$ 33.9	$ 27.3
Future Income Tax Benefit	7.3	8.9	7.0
The Connecticut Light and Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	8.8	10.9	9.8
Future Income Tax Benefit	2.3	2.9	2.5
NSTAR Electric Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	9.0	11.3	9.7
Future Income Tax Benefit	2.3	3.0	2.5
Public Service Company of New Hampshire
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation Expense	3.0	3.6	3.3
Future Income Tax Benefit	$ 0.8	$ 1.0	$ 0.8