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COMMITMENTS, GUARANTEES AND CONTINGENCIES - Other Matters (Details) $ in Millions | 1 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Aug. 06, 2024 complaint | Sep. 30, 2023 USD ($) | Sep. 30, 2024 USD ($)
Guarantor Obligations [Line Items] |  |  |
Production tax credits sold |  |  | $ 61.5
Number of complaints | complaint | 2 |  |
Gross proceeds from arbitration |  | $ 68.3 |
Prejudgment interest from legal settlements |  | 5.1 |
Arbitration costs recovery |  | 3.6 |
Pre tax gain from legal settlements |  | 58.4 |
Proceeds from arbitration ruling |  | $ 60.0 |
ALLETE, Inc. | Standby Letters of Credit |  |  |
Guarantor Obligations [Line Items] |  |  |
Letters of credit outstanding |  |  | 140.0
ALLETE, Inc. | Surety Bonds |  |  |
Guarantor Obligations [Line Items] |  |  |
Letters of credit outstanding |  |  | 105.1
Regulated Operations |  |  |
Guarantor Obligations [Line Items] |  |  |
Standby letters of credit and surety bonds outstanding |  |  | 31.3
ALLETE Clean Energy |  |  |
Guarantor Obligations [Line Items] |  |  |
Standby letters of credit and surety bonds outstanding |  |  | 81.6
BNI Energy Reclamation Liability |  |  |
Guarantor Obligations [Line Items] |  |  |
Estimated obligation |  |  | 82.1
BNI Energy Reclamation Liability | Surety Bonds |  |  |
Guarantor Obligations [Line Items] |  |  |
Collateral |  |  | 82.4
ALLETE South Wind | Standby Letters of Credit |  |  |
Guarantor Obligations [Line Items] |  |  |
Letters of credit outstanding |  |  | 10.1
South Shore Energy | Standby Letters of Credit |  |  |
Guarantor Obligations [Line Items] |  |  |
Letters of credit outstanding |  |  | 29.7
New Energy | Surety Bonds |  |  |
Guarantor Obligations [Line Items] |  |  |
Collateral |  |  | $ 10.0

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