DERIVATIVE INSTRUMENTS - Narrative (Details) - MW	6 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
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)	674	674
Level 3 | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts (in percentage)	1.80%
Level 3 | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts (in percentage)	6.10%
Level 3 | Weighted Average
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts (in percentage)	5.00%
CL&P
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts (in percent)	80.00%