EMPLOYEE BENEFITS - Schedule of Prepaid Assets (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	$ 1,511.2	$ 1,336.6
Less: Accrued SERP - current portion	13.3	24.0
Accrued SERP and PBOP	(100.9)	(95.4)
CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	204.1	182.5
Less: Accrued SERP - current portion	0.3	0.4
Accrued SERP and PBOP	(5.5)	(5.3)
NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	804.1	724.7
Less: Accrued SERP - current portion	0.0	0.2
Accrued SERP and PBOP	(1.7)	(2.0)
PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	111.8	91.0
Less: Accrued SERP - current portion	0.4	0.4
Accrued SERP and PBOP	(4.2)	(4.1)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	982.0	887.7
Pension Plan | CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	182.4	167.2
Pension Plan | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	404.0	376.9
Pension Plan | PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	97.0	80.5
PBOP
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	529.2	448.9
Accrued liability, defined benefit pension plan	(2.0)	0.0
PBOP | CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	21.7	15.3
Accrued liability, defined benefit pension plan	0.0	0.0
PBOP | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	400.1	347.8
Accrued liability, defined benefit pension plan	0.0	0.0
PBOP | PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	14.8	10.5
Accrued liability, defined benefit pension plan	0.0	0.0
SERP
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	(112.2)	(119.4)
SERP | CL&P
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	(5.8)	(5.7)
SERP | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	(1.7)	(2.2)
SERP | PSNH
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	$ (4.6)	$ (4.5)