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Operations and Significant Accounting Policies - Business Segments (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 USD ($) Customers MW | Dec. 31, 2021
Business Segments [Line Items] |  |
Number of Reportable Segments | 2 | 3
Square Butte [Member] | Square Butte PPA [Member] |  |
Business Segments [Line Items] |  |
Minnesota Power Output Entitlement (MW) | MW | 227.5 |
Nemadji Trail Energy Center [Member] |  |
Business Segments [Line Items] |  |
Estimated Capital Expenditures, Including Past Expenditures | $ | $ 700 |
Square Butte [Member] | Square Butte [Member] | Square Butte PPA [Member] |  |
Business Segments [Line Items] |  |
Generating Capacity Counterparty Owned (MW) | MW | 455 |
Minnesota Power [Member] | Square Butte [Member] | Square Butte [Member] | Square Butte PPA [Member] |  |
Business Segments [Line Items] |  |
Expected Output Entitlement (Percent) | 50.00% |
South Shore Energy | Nemadji Trail Energy Center [Member] |  |
Business Segments [Line Items] |  |
Capital Cost Spent to Date | $ | $ 7 |
Estimated Capital Expenditures, ALLETE Portion | $ | $ 150 |
New Energy |  |
Business Segments [Line Items] |  |
Discount Rate - Input for Goodwill Analysis | 14.00% |
Terminal Growth Rate - Input for Goodwill Analysis | 3.50% |
Regulated Operations [Member] | Minnesota Power [Member] | Retail Customers [Member] | Electric Rates [Member] |  |
Business Segments [Line Items] |  |
Number of Customers | 150,000 |
Regulated Operations [Member] | Minnesota Power [Member] | Municipal Customers [Member] | Electric Rates [Member] |  |
Business Segments [Line Items] |  |
Number of Customers | 14 |
Regulated Operations [Member] | SWL&P [Member] | Retail Customers [Member] | Electric Rates [Member] |  |
Business Segments [Line Items] |  |
Number of Customers | 15,000 |
Regulated Operations [Member] | SWL&P [Member] | Retail Customers [Member] | Natural Gas [Member] |  |
Business Segments [Line Items] |  |
Number of Customers | 13,000 |
Regulated Operations [Member] | SWL&P [Member] | Retail Customers [Member] | Water [Member] |  |
Business Segments [Line Items] |  |
Number of Customers | 10,000 |
ALLETE Clean Energy [Member] | ALLETE Clean Energy [Member] |  |
Business Segments [Line Items] |  |
Energy Generation Owned (MW) | MW | 1,200 |
Generating Capacity Under Construction (MW) | MW | 100 |
Corporate and Other [Member] | BNI Energy [Member] |  |
Business Segments [Line Items] |  |
Number of Customers | 2 |
Corporate and Other [Member] | BNI Energy [Member] | Square Butte [Member] |  |
Business Segments [Line Items] |  |
Number of Customers | 1 |
Nobles 2 [Member] |  |
Business Segments [Line Items] |  |
Ownership Percentage | 49.00% |
Natural Gas-Fired [Member] | Nemadji Trail Energy Center [Member] |  |
Business Segments [Line Items] |  |
Generating Capacity Jointly Owned (MW) | MW | 600 |
Natural Gas-Fired [Member] | South Shore Energy | Nemadji Trail Energy Center [Member] |  |
Business Segments [Line Items] |  |
Expected Output Entitlement (Percent) | 20.00% |
Wind Turbine Generators [Member] | Minnesota Power [Member] | Tenaska [Member] | Nobles 2 PPA [Member] |  |
Business Segments [Line Items] |  |
Generating Capacity Counterparty Owned (MW) | MW | 250 |
Contract Term (Years) | 20 years |

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