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v3.22.4

Short-Term and Long-Term Debt - Long-Term Debt (Details) $ in Millions |  |  | 12 Months Ended
--- | --- | --- | ---
Aug. 09, 2022 USD ($) | Feb. 28, 2022 USD ($) | Dec. 31, 2022 USD ($) Years | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
Debt Instrument [Line Items] |  |  |  |  |
Long-Term Debt |  |  | $ 1,648.2 | $ 1,763.2 |
Long-Term Debt - Unamortized Debt Issuance Costs |  |  | 8.2 |  |
Debt Instrument [Abstract] |  |  |  |  |
Long-Term Debt Maturing in 2022 |  |  | 91.9 |  |
Long-Term Debt Maturing in 2023 |  |  | 94.8 |  |
Long-Term Debt Maturing in 2024 |  |  | 386.1 |  |
Long-Term Debt Maturing in 2025 |  |  | 79.4 |  |
Long-Term Debt Maturing in 2026 |  |  | 122.5 |  |
Long-Term Debt Maturing Thereafter |  |  | 1,154.4 |  |
Proceeds from Non-Controlling Interest - Net of Issuance Costs |  |  | 155.7 | $ 90.9 | $ 414.5
Camp Ripley Financing [Member] |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Annual Financing Payment |  |  | $ 1.4 |  |
Financing Renewal Term (Years) | Years |  |  | 2 |  |
Purchase Option |  |  | $ 4.0 |  |
First Mortgage Bonds - 2.50% Due August 2030 [Member] |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Interest Rate |  |  | 4.08% |  |
First Mortgage Bonds - 4.47% Series Due 2049 [Member] |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Interest Rate |  |  | 4.47% |  |
First Mortgage Bonds - 4.07% Series Due 2048 [Member] |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Interest Rate |  |  | 4.07% |  |
ALLETE Senior Unsecured Notes 3.11% Due 2027 [Member] |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Interest Rate |  |  | 3.11% |  |
First Mortgage Bonds - 2.50% Series Due 2030 |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Interest Rate |  |  | 2.50% |  |
First Mortgage Bonds - 3.30% Series Due 2050 |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Interest Rate |  |  | 3.30% |  |
March Unsecured Term Loan Due in 2023 |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Unsecured Term Loan, Amount |  |  | $ 170.0 |  |
Debt Instrument, Description of Variable Rate Basis |  |  | SOFR |  |
Debt Instrument, Basis Spread on Variable Rate |  |  | 0.75% |  |
ALLETE Bonds 4.54% Due August 2032 |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Proceeds from Issuance of First Mortgage Bond | $ 75.0 |  |  |  |
Interest Rate | 4.54% |  |  |  |
February Unsecured Term Loan Terminated in April 2022 |  |  |  |  |
Debt Instrument [Abstract] |  |  |  |  |
Unsecured Term Loan, Amount |  | $ 175.0 |  |  |

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