INCOME TAXES - Tax Credits and Loss Carryforwards (Details) - State and Local Jurisdiction - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Operating Loss Carryforwards [Line Items]
State Net Operating Loss	$ 243.4	$ 288.1
State Tax Credit	228.5	204.5
State Charitable Contribution	7.9	20.1
CL&P
Operating Loss Carryforwards [Line Items]
State Net Operating Loss	0.0	0.0
State Tax Credit	157.5	137.7
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