DERIVATIVE INSTRUMENTS - Narrative (Details)	9 Months Ended
	Sep. 30, 2023 MW	Dec. 31, 2022 $ / KWmo 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	674	674
Level 3 | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts (in percentage)	1.30%
Level 3 | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts (in percentage)	5.50%
Level 3 | Weighted Average
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of exit price premiums related to derivative contracts (in percentage)	4.50%
CL&P
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Percentage of costs or benefits borne under capacity-related contracts (in percent)	80.00%
CL&P | Level 3 | Minimum | Measurement Input, Forward Reserve
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input		0.44
CL&P | Level 3 | Maximum | Measurement Input, Forward Reserve
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input		0.50
CL&P | Level 3 | Weighted Average | Measurement Input, Forward Reserve
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input		0.47