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COMMITMENTS AND CONTINGENCIES - Environmental Sites and Related Reserves (Details) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2025 USD ($) site | Dec. 31, 2024 USD ($) site
Site Contingency [Line Items] |  |
Number of Sites | site | 65 | 65
Reserve | $ | $ 152.2 | $ 128.0
CL&P |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 15 | 15
Reserve | $ | $ 13.8 | $ 13.4
NSTAR Electric |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 14 | 14
Reserve | $ | $ 8.3 | $ 6.6
PSNH |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 8 | 8
Reserve | $ | $ 9.1 | $ 6.3

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