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Business Segments - (Details) - USD ($) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023
Business Segments [Line Items] |  |  |
Total Operating Revenue | $ 403.3 | $ 564.9 |
Net Income Attributable to ALLETE | 50.7 | 58.2 |
Assets | 6,604.6 |  | $ 6,656.4
Corporate and Other |  |  |
Business Segments [Line Items] |  |  |
Total Operating Revenue | 403.3 | 564.9 |
Regulated Operations |  |  |
Business Segments [Line Items] |  |  |
Net Income Attributable to ALLETE | 44.2 | 40.6 |
Assets | 4,345.1 |  | 4,335.0
Regulated Operations | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Total Operating Revenue | 338.3 | 312.6 |
Regulated Operations | Residential | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 51.5 | 49.4 |
Regulated Operations | Commercial | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 49.7 | 47.7 |
Regulated Operations | Municipal | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 9.0 | 8.9 |
Regulated Operations | Industrial | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 159.5 | 144.9 |
Regulated Operations | Other Power Suppliers | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 40.0 | 35.9 |
Regulated Operations | Other | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 28.6 | 25.8 |
ALLETE Clean Energy |  |  |
Business Segments [Line Items] |  |  |
Net Income Attributable to ALLETE | 3.8 | 8.5 |
Assets | 1,580.0 |  | 1,594.1
ALLETE Clean Energy | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Total Operating Revenue | 19.1 | 201.5 |
ALLETE Clean Energy | Long-term PSA | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 17.8 | 18.4 |
ALLETE Clean Energy | Sale of Wind Energy Facilities | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 0.0 | 181.8 |
ALLETE Clean Energy | Other | Operating Segments |  |  |
Business Segments [Line Items] |  |  |
Operating revenue, other than customer revenue | 1.3 | 1.3 |
Corporate and Other |  |  |
Business Segments [Line Items] |  |  |
Net Income Attributable to ALLETE | 2.7 | 9.1 |
Assets | 679.5 |  | $ 727.3
Corporate and Other | Corporate and Other |  |  |
Business Segments [Line Items] |  |  |
Total Operating Revenue | 45.9 | 50.8 |
Corporate and Other | Long-term Contract | Corporate and Other |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 25.4 | 25.5 |
Corporate and Other | Sale of Renewable Development Projects | Corporate and Other |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 13.9 | 19.8 |
Corporate and Other | Other | Corporate and Other |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | $ 6.6 | $ 5.5 |

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