INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Tax liability related to the deferral of employer payroll tax liability provision of the CARES Act	$ 19.6	$ 39.0
Accrued interest payable	0.1	0.1
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Valuation allowance for tax credit and operating loss carryforward	61.5	48.3
State and Local Jurisdiction | The Connecticut Light and Power Company
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	10.8	8.8
Eversource | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Change in valuation allowance	$ 13.0	$ 10.3