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DERIVATIVE INSTRUMENTS - Narrative (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2022 USD ($) MW | Jun. 30, 2021 USD ($) | Jun. 30, 2022 USD ($) MW | Jun. 30, 2021 USD ($) | Dec. 31, 2021 $ / KWmo MW
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |  |  |
Percentage of costs or benefits borne under capacity-related contracts by United Illuminated Company |  |  | 20.00% |  |
Amount of power to be purchased under capacity-related contract (in MW) | MW | 675 |  | 675 |  | 675
Gains (losses) on deferred as regulatory costs | $ | $ 2.6 | $ 0.9 | $ 8.8 | $ (10.2) |
Level 3 | Minimum |  |  |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |  |  |
Percentage of exit price premiums related to derivative contracts |  |  | 3.90% |  |
Level 3 | Maximum |  |  |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |  |  |
Percentage of exit price premiums related to derivative contracts |  |  | 8.20% |  |
Level 3 | Weighted Average |  |  |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |  |  |
Percentage of exit price premiums related to derivative contracts |  |  | 7.10% |  |
CL&P |  |  |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |  |  |
Percentage of costs or benefits borne under capacity-related contracts |  |  | 80.00% |  |
CL&P | Weighted Average | Measurement Input, Capacity Prices |  |  |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |  |  |
Derivative measurement input | $ / KWmo |  |  |  |  | 2.61

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