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COMMITMENTS AND CONTINGENCIES - Schedule of Reconciliation of Activity in Environmental Reserve (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020
Accrual for Environmental Loss Contingencies [Roll Forward] |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | $ 102.4 | $ 81.0
Increase Due to CMA Asset Acquisition |  | 22.9
Additions | 23.4 | 8.4
Payments/Reductions | (10.4) | (9.9)
Accrual for Environmental Loss Contingencies, Ending Balance | 115.4 | 102.4
The Connecticut Light and Power Company |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | 12.3 | 11.4
Increase Due to CMA Asset Acquisition |  | 0.0
Additions | 4.4 | 4.2
Payments/Reductions | (2.8) | (3.3)
Accrual for Environmental Loss Contingencies, Ending Balance | 13.9 | 12.3
NSTAR Electric Company |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | 4.7 | 8.0
Increase Due to CMA Asset Acquisition |  | 0.0
Additions | 0.0 | 0.7
Payments/Reductions | (1.4) | (4.0)
Accrual for Environmental Loss Contingencies, Ending Balance | 3.3 | 4.7
Public Service Company of New Hampshire |  |
Accrual for Environmental Loss Contingencies [Roll Forward] |  |
Accrual for Environmental Loss Contingencies, Beginning Balance | 7.1 | 7.5
Increase Due to CMA Asset Acquisition |  | 0.0
Additions | 0.0 | 0.0
Payments/Reductions | (0.8) | (0.4)
Accrual for Environmental Loss Contingencies, Ending Balance | $ 6.3 | $ 7.1

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