EMPLOYEE BENEFITS - Schedule of Funded Status (Details) - Pension Plan - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 6,337.3	$ 6,669.4
The Connecticut Light and Power Company
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,241.1	1,356.4
NSTAR Electric Company
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	1,376.1	1,449.4
Public Service Company of New Hampshire
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 670.3	$ 707.2