EMPLOYEE BENEFITS - Schedule of Other Retirement Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	$ 43.4	$ 42.8	$ 45.7
Other Retirement Benefits Expense	10.9	2.2	3.3
Retirement benefit payable	9.2
CL&P
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.2	0.2	0.2
Other Retirement Benefits Expense	4.0	0.7	1.2
NSTAR Electric
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.1	0.1	0.1
Other Retirement Benefits Expense	3.7	0.7	1.1
PSNH
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	1.3	1.5	1.7
Other Retirement Benefits Expense	$ 1.3	$ 0.3	$ 0.5