EMPLOYEE BENEFITS - Pension Plan Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2026	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Defined Contribution Plan Disclosure [Line Items]
Expected Long-Term Rate of Return (in percent)		8.25%	8.25%	7.94%
Eversource Service Pension and PBOP Plans
Defined Contribution Plan Disclosure [Line Items]
Assumed Rate of Return on Defined Benefit Plan Assets		8.25%
Pension and SERP
Defined Contribution Plan Disclosure [Line Items]
Increase of liability as a result of change in discount rate		$ 98.2	$ 332.9
Defined benefit plan, loss due to updated census data		38.1	$ 42.1
Defined benefit plan, loss due to salary scale assumption		$ 28.0
Expected Long-Term Rate of Return (in percent)		8.25%	8.25%	8.25%
Employer Contributions		$ 2.5	$ 5.0
Pension and SERP | Forecast
Defined Contribution Plan Disclosure [Line Items]
Employer Contributions	$ 2.5
PBOP
Defined Contribution Plan Disclosure [Line Items]
Increase of liability as a result of change in discount rate		$ 11.2
Decrease in liability as a result of a change in discount rate			$ 39.8
Expected Long-Term Rate of Return (in percent)		8.25%	8.25%	8.25%
Employer Contributions		$ 0.7	$ 0.9
PBOP | Forecast
Defined Contribution Plan Disclosure [Line Items]
Employer Contributions	$ 2.8
PBOP | Aquarion
Defined Contribution Plan Disclosure [Line Items]
Expected Long-Term Rate of Return (in percent)		7.00%	7.00%
PBOP | Pre-65 Plan
Defined Contribution Plan Disclosure [Line Items]
Health care trend rate		7.25%
Ultimate rate		5.00%
PBOP | Pre-65 Plan | Aquarion | Minimum
Defined Contribution Plan Disclosure [Line Items]
Health care trend rate		3.50%	3.50%	3.50%
PBOP | Pre-65 Plan | Aquarion | Maximum
Defined Contribution Plan Disclosure [Line Items]
Health care trend rate		7.50%	6.75%	7.00%
PBOP | Post-65 Plan
Defined Contribution Plan Disclosure [Line Items]
Ultimate rate		3.50%