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COMMITMENTS AND CONTINGENCIES - Environmental Sites and Related Reserves (Details) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2022 USD ($) site | Dec. 31, 2021 USD ($) site
Site Contingency [Line Items] |  |
Number of Sites | site | 62 | 61
Reserve | $ | $ 121.3 | $ 115.4
CL&P |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 14 | 14
Reserve | $ | $ 14.3 | $ 13.9
NSTAR Electric |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 11 | 11
Reserve | $ | $ 3.6 | $ 3.3
PSNH |  |
Site Contingency [Line Items] |  |
Number of Sites | site | 9 | 9
Reserve | $ | $ 6.3 | $ 6.3

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