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COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Long-term Purchase Commitment [Line Items] |  |  |
Renewable Energy Purchase Contracts | $ 581.4 | $ 678.1 | $ 609.2
Natural Gas Procurement | 695.8 | 1,042.8 | 712.7
Purchased Power and Capacity | 69.0 | 61.6 | 56.4
Peaker CfDs | 20.1 | 13.4 | 24.3
Transmission Support Commitments | 14.2 | 12.7 | 15.4
CL&P |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Renewable Energy Purchase Contracts | 474.1 | 513.2 | 457.1
Purchased Power and Capacity | 65.5 | 57.7 | 53.1
Peaker CfDs | 20.1 | 13.4 | 24.3
Transmission Support Commitments | 5.6 | 5.0 | 6.1
NSTAR Electric |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Renewable Energy Purchase Contracts | 60.0 | 90.8 | 84.7
Purchased Power and Capacity | 2.9 | 3.0 | 3.0
Peaker CfDs | 0.0 | 0.0 | 0.0
Transmission Support Commitments | 5.6 | 5.0 | 6.0
PSNH |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Renewable Energy Purchase Contracts | 47.3 | 74.1 | 67.4
Purchased Power and Capacity | 0.6 | 0.9 | 0.3
Peaker CfDs | 0.0 | 0.0 | 0.0
Transmission Support Commitments | $ 3.0 | $ 2.7 | $ 3.3

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