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COMMITMENTS, GUARANTEES AND CONTINGENCIES - Other Matters (Details) $ in Millions	1 Months Ended
	Aug. 06, 2024 complaint	Mar. 31, 2025 USD ($)
Guarantor Obligations [Line Items]
Production tax credits sold		$ 77.6
Number of complaints | complaint	3
ALLETE, Inc. | Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		142.8
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		37.9
ALLETE Clean Energy
Guarantor Obligations [Line Items]
Standby letters of credit and surety bonds outstanding		86.6
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		10.1
South Shore Energy | Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		29.7
New Energy | Standby Letters of Credit
Guarantor Obligations [Line Items]
Collateral		$ 11.9

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 4
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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