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v3.25.2

DERIVATIVE INSTRUMENTS - Narrative (Details) $ in Millions | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | ---
Jul. 31, 2025 USD ($) | Jun. 30, 2025 USD ($) MW | Jun. 30, 2024 USD ($) | Jun. 30, 2025 USD ($) MW | Jun. 30, 2024 USD ($) | Dec. 31, 2024 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 |  | 609 |  | 609 |  | 610
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 losses recognized in regulatory asset liability |  | $ 0.3 | $ 1.9 | $ 0.6 | $ 2.9 |
NSTAR Electric | Subsequent Event |  |  |  |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |  |  |  |
Derivative, term of contract | 20 years |  |  |  |  |
Derivative, notional amount | $ 6,700.0 |  |  |  |  |

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