DERIVATIVE INSTRUMENTS - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) MW	Mar. 31, 2023 USD ($)	Dec. 31, 2023 MW
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts by United Illuminated Company (in percent)	20.00%
Amount of power to be purchased under capacity-related contract (in MW) | MW	682		682
CL&P
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts (in percent)	80.00%
Derivative instruments gain (loss) recognized in regulatory asset liability | $	$ (1.0)	$ (1.9)