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COMMITMENTS AND CONTINGENCIES - Environmental Sites and Related Reserves (Details) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2024 USD ($) site | Dec. 31, 2023 USD ($) site
Site Contingency [Line Items] |  |
Number of Sites | site | 65 | 65
Reserve | $ | $ 130.5 | $ 128.2
CL&P |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 15 | 16
Reserve | $ | $ 13.7 | $ 13.8
NSTAR Electric |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 13 | 12
Reserve | $ | $ 6.7 | $ 5.4
PSNH |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 8 | 8
Reserve | $ | $ 6.4 | $ 7.6

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