EMPLOYEE BENEFITS - Schedule of Other Retirement Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	$ 29.9	$ 30.2	$ 32.6
Other Retirement Benefits Expense	2.3	2.4	2.6
CL&P
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.1	0.1	0.2
Other Retirement Benefits Expense	0.8	0.8	0.8
NSTAR Electric
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	0.0	0.0	0.0
Other Retirement Benefits Expense	0.8	0.8	0.8
PSNH
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarially-Determined Liability	1.0	1.0	1.1
Other Retirement Benefits Expense	$ 0.3	$ 0.3	$ 0.4