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REGULATORY MATTERS - Electric Rates (Details) - USD ($) $ in Thousands |  |  |  |  |  | 3 Months Ended | 9 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
May 03, 2024 | Apr. 01, 2024 | Mar. 29, 2024 | Dec. 19, 2023 | Nov. 01, 2023 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023 | Dec. 31, 2023
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Regulatory Assets |  |  |  |  |  |  | $ 386,100 |  | $ 425,400
ECO Annual Filing Member | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Revenue from cost recovery riders and other regulatory programs |  | $ 2,200 |  |  |  | $ 2,200 |  |  |
Electric Rates | Fuel Adjustment Clause 2023 | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Regulatory Assets |  |  |  |  |  |  |  |  | $ 13,000
Retail Customers | Electric Rates | Current Cost Recovery Rider | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Revenue from cost recovery riders and other regulatory programs |  |  |  |  |  |  | 15,100 | $ 44,900 |
Retail Customers | Electric Rates | 2024 Minnesota General Rate Case | MPUC | Minnesota Power |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Requested rate increase percent |  |  |  |  | 12.00% |  |  |  |
Requested return on equity | 9.78% |  |  |  | 10.30% |  |  |  |
Requested equity capital structure |  |  |  |  | 53.00% |  |  |  |
Annual additional revenue generated from requested final rate increase | $ 33,970 |  |  |  | $ 89,000 |  |  |  |
Approved rate increase |  |  |  | $ 64,000 |  |  |  |  |
Regulatory liabilities |  |  |  |  |  |  | $ 17,000 |  |
Retail Customers | Electric Rates | 2024 Wisconsin General Rate Case | PSCW | SWL&P |  |  |  |  |  |  |  |  |
Regulatory Matters [Line Items] |  |  |  |  |  |  |  |  |
Requested rate increase percent |  |  | 5.90% |  |  |  |  |  |
Requested return on equity |  |  | 10.00% |  |  |  |  |  |
Requested equity capital structure |  |  | 55.00% |  |  |  |  |  |
Annual additional revenue generated from requested final rate increase |  |  | $ 7,300 |  |  |  |  |  |

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