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COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Accrual for Environmental Loss Contingencies [Roll Forward] |  |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | $ 115.4 | $ 102.4 |
Additions | 12.6 | 23.4 |
Payments/Reductions | (5.4) | (10.4) |
Accrual for Environmental Loss Contingencies, Ending Balance | $ 122.6 | $ 115.4 |
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 | $ 12.3 |
Additions | 0.9 | 4.4 |
Payments/Reductions | (0.9) | (2.8) |
Accrual for Environmental Loss Contingencies, Ending Balance | 13.9 | 13.9 |
NSTAR Electric |  |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | 3.3 | 4.7 |
Additions | 0.4 | 0.0 |
Payments/Reductions | (0.3) | (1.4) |
Accrual for Environmental Loss Contingencies, Ending Balance | 3.4 | 3.3 |
PSNH |  |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | 6.3 | 7.1 |
Additions | 0.5 | 0.0 |
Payments/Reductions | (0.7) | (0.8) |
Accrual for Environmental Loss Contingencies, Ending Balance | $ 6.1 | $ 6.3 |

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