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v3.22.1

Business Segments (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2022 USD ($) Segments | Mar. 31, 2021 USD ($) | Dec. 31, 2021 USD ($)
Business Segments [Line Items] |  |  |
Number of Reportable Segments | Segments | 2 |  |
Operating Revenue | $ 383.5 | $ 339.2 |
Net Income (Loss) Attributable to ALLETE | 66.3 | 51.8 |
Assets | $ 6,556.0 |  | $ 6,435.0
Regulated Operations [Member] |  |  |
Business Segments [Line Items] |  |  |
Number of Operating Segments | Segments | 3 |  |
Operating Revenue | $ 329.0 | 293.0 |
Net Income (Loss) Attributable to ALLETE | 51.5 | 45.0 |
Assets | 4,297.1 |  | 4,289.4
Regulated Operations [Member] | Residential [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 56.0 | 45.6 |
Regulated Operations [Member] | Commercial [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 48.3 | 39.7 |
Regulated Operations [Member] | Municipal [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 12.1 | 12.6 |
Regulated Operations [Member] | Industrial [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 147.8 | 129.0 |
Regulated Operations [Member] | Other Power Suppliers [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 41.0 | 38.4 |
Regulated Operations [Member] | Other [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 23.8 | 27.7 |
ALLETE Clean Energy [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 28.2 | 20.9 |
Net Income (Loss) Attributable to ALLETE | 16.5 | 7.4 |
Assets | 1,816.1 |  | 1,719.4
ALLETE Clean Energy [Member] | Long-term PSA [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 25.4 | 18.1 |
ALLETE Clean Energy [Member] | Other [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue, Other Than Customer Revenue | $ 2.8 | 2.8 |
Corporate and Other [Member] |  |  |
Business Segments [Line Items] |  |  |
Number of Operating Segments | Segments | 2 |  |
Operating Revenue | $ 26.3 | 25.3 |
Net Income (Loss) Attributable to ALLETE | (1.7) | (0.6) |
Assets | 442.8 |  | $ 426.2
Corporate and Other [Member] | Long-term Contract [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 22.6 | 21.7 |
Corporate and Other [Member] | Other [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | $ 3.7 | $ 3.6 |

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