INCOME TAXES - Tax Credits and Loss Carryforwards (Details) - State and Local Jurisdiction - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
State Net Operating Loss	$ 288.1	$ 138.3
State Tax Credit	204.5	197.7
State Charitable Contribution	20.1	23.7
CL&P
Operating Loss Carryforwards [Line Items]
State Net Operating Loss	0.0	0.0
State Tax Credit	137.7	137.0
State Charitable Contribution	0.0	0.0
NSTAR Electric
Operating Loss Carryforwards [Line Items]
State Net Operating Loss	0.0	0.0
State Tax Credit	0.0	0.0
State Charitable Contribution	0.0	0.0
PSNH
Operating Loss Carryforwards [Line Items]
State Net Operating Loss	0.0	0.0
State Tax Credit	0.0	0.0
State Charitable Contribution	$ 0.0	$ 0.0