EMPLOYEE BENEFITS - Schedule of Defined Contribution Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 55.5	$ 49.4	$ 41.6
The Connecticut Light and Power Company
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	7.0	6.6	5.5
NSTAR Electric Company
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	12.2	11.8	10.3
Public Service Company of New Hampshire
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 4.3	$ 4.1	$ 3.5