EMPLOYEE BENEFITS - Schedule of Prepaid Assets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	$ 1,028.2	$ 1,045.5
Less: Accrued SERP - current portion	(19.4)	(47.3)
Accrued Pension, SERP and PBOP	123.8	135.5
CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	129.8	147.9
Less: Accrued SERP - current portion	(0.3)	(0.3)
Accrued Pension, SERP and PBOP	5.6	12.9
NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	608.6	576.8
Less: Accrued SERP - current portion	(0.2)	(0.2)
Accrued Pension, SERP and PBOP	1.7	1.6
PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	59.0	66.4
Less: Accrued SERP - current portion	(0.4)	(0.4)
Accrued Pension, SERP and PBOP	4.2	6.5
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	672.2	756.7
Accrued liability, defined benefit pension plan	0.0	3.7
Pension Plan | CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	127.4	147.9
Accrued liability, defined benefit pension plan	0.0	0.0
Pension Plan | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	306.5	310.2
Accrued liability, defined benefit pension plan	0.0	0.0
Pension Plan | PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	56.3	66.4
Accrued liability, defined benefit pension plan	0.0	0.0
PBOP
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	356.0	288.8
Accrued liability, defined benefit pension plan	7.6	12.4
PBOP | CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	2.4	0.0
Accrued liability, defined benefit pension plan	0.0	7.3
PBOP | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	302.1	266.6
Accrued liability, defined benefit pension plan	0.0	0.0
PBOP | PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	2.7	0.0
Accrued liability, defined benefit pension plan	0.0	2.3
SERP
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	135.6	166.7
SERP | CL&P
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	5.9	5.9
SERP | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	1.9	1.8
SERP | PSNH
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	$ 4.6	$ 4.6