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COMMITMENTS, GUARANTEES AND CONTINGENCIES - Other Matters (Details) $ in Millions | 1 Months Ended |
--- | --- | ---
Aug. 06, 2024 complaint | Sep. 30, 2025 USD ($)
Guarantor Obligations [Line Items] |  |
Production tax credits sold |  | $ 93.3
Number of complaints | complaint | 3 |
ALLETE, Inc. | Standby Letters of Credit |  |
Guarantor Obligations [Line Items] |  |
Letters of credit outstanding |  | 136.8
ALLETE, Inc. | Surety Bonds |  |
Guarantor Obligations [Line Items] |  |
Letters of credit outstanding |  | 133.2
Regulated Operations |  |
Guarantor Obligations [Line Items] |  |
Standby letters of credit and surety bonds outstanding |  | 33.9
ALLETE Clean Energy |  |
Guarantor Obligations [Line Items] |  |
Standby letters of credit and surety bonds outstanding |  | 86.2
New Energy | Standby Letters of Credit |  |
Guarantor Obligations [Line Items] |  |
Collateral |  | 10.4
BNI Energy Reclamation Liability |  |
Guarantor Obligations [Line Items] |  |
Estimated obligation |  | 99.5
BNI Energy Reclamation Liability | Surety Bonds |  |
Guarantor Obligations [Line Items] |  |
Collateral |  | 99.7
ALLETE South Wind | Standby Letters of Credit |  |
Guarantor Obligations [Line Items] |  |
Letters of credit outstanding |  | 29.7
South Shore Energy | Standby Letters of Credit |  |
Guarantor Obligations [Line Items] |  |
Letters of credit outstanding |  | $ 10.1

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