EMPLOYEE BENEFITS - Schedule of Prepaid Assets (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	$ 1,045.5	$ 272.0
Less: Accrued SERP - current portion	(47.3)	(9.7)
Accrued Pension, SERP and PBOP	135.5	242.5
CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	147.9	0.4
Less: Accrued SERP - current portion	(0.3)	(0.5)
Accrued Pension, SERP and PBOP	12.9	26.8
NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	576.8	441.4
Less: Accrued SERP - current portion	(0.2)	(0.2)
Accrued Pension, SERP and PBOP	1.6	2.0
PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	66.4	0.0
Less: Accrued SERP - current portion	(0.4)	(0.5)
Accrued Pension, SERP and PBOP	6.5	30.2
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	756.7	0.0
Accrued liability, defined benefit pension plan	3.7	58.1
Pension Plan | CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	147.9	0.4
Accrued liability, defined benefit pension plan	0.0	0.0
Pension Plan | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	310.2	149.8
Accrued liability, defined benefit pension plan	0.0	0.0
Pension Plan | PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	66.4	0.0
Accrued liability, defined benefit pension plan	0.0	20.6
PBOP
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	288.8	272.0
Accrued liability, defined benefit pension plan	12.4	18.0
PBOP | CL&P
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	0.0	0.0
Accrued liability, defined benefit pension plan	7.3	19.8
PBOP | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	266.6	291.6
Accrued liability, defined benefit pension plan	0.0	0.0
PBOP | PSNH
Defined Benefit Plan Disclosure [Line Items]
Prepaid asset	0.0	0.0
Accrued liability, defined benefit pension plan	2.3	4.3
SERP
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	166.7	176.1
SERP | CL&P
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	5.9	7.5
SERP | NSTAR Electric
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	1.8	2.2
SERP | PSNH
Defined Benefit Plan Disclosure [Line Items]
Accrued liability, defined benefit pension plan	$ 4.6	$ 5.8