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Business Segment - By Chanel (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2024 | Sep. 30, 2024 | Jun. 30, 2024 | Mar. 31, 2024 | Dec. 31, 2023 | Sep. 30, 2023 | Jun. 30, 2023 | Mar. 31, 2023 | Dec. 31, 2022 | Sep. 30, 2022 | Jun. 30, 2022 | Mar. 31, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue | $ 364.8 | $ 407.2 | $ 354.5 | $ 403.3 | $ 402.7 | $ 378.8 | $ 533.4 | $ 564.9 | $ 425.8 | $ 388.3 | $ 373.1 | $ 383.5 | $ 1,529.8 | $ 1,879.8 | $ 1,570.7
Other |  |  |  |  |  |  |  |  |  |  |  |  | 5.0 | 5.1 | 7.6
Net Income Attributable to ALLETE | $ 50.6 | $ 45.0 | $ 33.0 | $ 50.7 | $ 51.5 | $ 85.9 | $ 51.5 | $ 58.2 | $ 51.7 | $ 33.7 | $ 37.6 | $ 66.3 | 179.3 | 247.1 | 189.3
New Energy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition related costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.7
Regulated Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 1,242.7 | 1,238.3 | 1,259.3
Net Income Attributable to ALLETE |  |  |  |  |  |  |  |  |  |  |  |  | 160.9 | 147.2 | 149.9
ALLETE Clean Energy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 84.3 | 418.5 | 118.3
Net Income Attributable to ALLETE |  |  |  |  |  |  |  |  |  |  |  |  | 17.8 | 71.7 | 16.3
Gain From Legal Settlements - after-tax |  |  |  |  |  |  |  |  |  |  |  |  |  | 44.3 |
Corporate and Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 202.8 | 223.0 | 193.1
Net Income Attributable to ALLETE |  |  |  |  |  |  |  |  |  |  |  |  | 0.6 | 28.2 | 23.1
Purchase price accounting - after tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.3
Acquisition related costs |  |  |  |  |  |  |  |  |  |  |  |  | 22.6 |  |
Corporate and Other | New Energy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition related costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.7
Residential | Regulated Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 177.0 | 165.7 | 175.9
Commercial | Regulated Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 189.8 | 184.6 | 187.2
Municipal | Regulated Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 34.2 | 33.4 | 40.2
Industrial | Regulated Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 610.8 | 593.6 | 589.0
Other Power Suppliers | Regulated Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 137.2 | 146.1 | 165.8
Other | Regulated Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 93.7 | 114.9 | 101.2
Long-term PSA | ALLETE Clean Energy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 56.4 | 65.0 | 77.2
Sale of Wind Energy Facilities | ALLETE Clean Energy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 22.9 | 348.4 | 33.5
Other | ALLETE Clean Energy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other |  |  |  |  |  |  |  |  |  |  |  |  | 5.0 | 5.1 | 7.6
Long-term Contract | Corporate and Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 105.7 | 101.2 | 89.2
Sale of Renewable Development Projects | Corporate and Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | 72.1 | 92.5 | 73.9
Other | Corporate and Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  |  |  |  |  | $ 25.0 | $ 29.3 | $ 30.0

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