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v3.21.1

Business Segments (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 USD ($) a Segments | Mar. 31, 2020 USD ($) | Dec. 31, 2020 USD ($)
Business Segments [Line Items] |  |  |
Number of Reportable Segments | Segments | 2 |  |
Operating Revenue | $ 339.2 | $ 311.6 |
Net Income (Loss) Attributable to ALLETE | 51.8 | 66.3 |
Assets | $ 6,274.5 |  | $ 6,084.6
Regulated Operations [Member] |  |  |
Business Segments [Line Items] |  |  |
Number of Operating Segments | Segments | 3 |  |
Operating Revenue | $ 293.0 | 265.3 |
Net Income (Loss) Attributable to ALLETE | 45.0 | 57.5 |
Assets | 4,184.1 |  | 4,196.8
Regulated Operations [Member] | Residential [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 45.6 | 40.9 |
Regulated Operations [Member] | Commercial [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 39.7 | 37.3 |
Regulated Operations [Member] | Municipal [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 12.6 | 10.3 |
Regulated Operations [Member] | Industrial [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 129.0 | 118.8 |
Regulated Operations [Member] | Other Power Suppliers [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 38.4 | 38.3 |
Regulated Operations [Member] | Other [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 27.7 | 19.7 |
ALLETE Clean Energy [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 20.9 | 20.1 |
Net Income (Loss) Attributable to ALLETE | 7.4 | 11.7 |
Assets | 1,596.6 |  | 1,483.3
ALLETE Clean Energy [Member] | Long-term PSA [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 18.1 | 17.3 |
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 |  |
Land in Minnesota (Acres) | a | 4,000 |  |
Operating Revenue | $ 25.3 | 26.2 |
Net Income (Loss) Attributable to ALLETE | (0.6) | (2.9) |
Assets | 493.8 |  | $ 404.5
Corporate and Other [Member] | Long-term Contract [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | 21.7 | 22.4 |
Corporate and Other [Member] | Other [Member] |  |  |
Business Segments [Line Items] |  |  |
Operating Revenue | $ 3.6 | $ 3.8 |

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