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COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Accrual for Environmental Loss Contingencies [Roll Forward] |  |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | $ 122.6 | $ 115.4 |
Additions | 16.8 | 12.6 |
Payments/Reductions | (11.2) | (5.4) |
Accrual for Environmental Loss Contingencies, Ending Balance | $ 128.2 | $ 122.6 |
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration] | Other Current Liabilities | Other Current Liabilities | Other Current Liabilities
CL&P |  |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | $ 13.9 | $ 13.9 |
Additions | 2.6 | 0.9 |
Payments/Reductions | (2.7) | (0.9) |
Accrual for Environmental Loss Contingencies, Ending Balance | 13.8 | 13.9 |
NSTAR Electric |  |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | 3.4 | 3.3 |
Additions | 2.5 | 0.4 |
Payments/Reductions | (0.5) | (0.3) |
Accrual for Environmental Loss Contingencies, Ending Balance | 5.4 | 3.4 |
PSNH |  |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | 6.1 | 6.3 |
Additions | 1.7 | 0.5 |
Payments/Reductions | (0.2) | (0.7) |
Accrual for Environmental Loss Contingencies, Ending Balance | $ 7.6 | $ 6.1 |

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