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Commitments, Guarantees and Contingencies - Other Matters (Details) - USD ($) $ in Millions	Apr. 30, 2024	Mar. 31, 2024
Subsequent Event
Guarantor Obligations [Line Items]
Production tax credits sold	$ 14.0
ALLETE, Inc. | Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		$ 150.1
Regulated Operations | Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		25.4
ALLETE Clean Energy | Standby Letters of Credit
Guarantor Obligations [Line Items]
Letters of credit outstanding		80.6
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

X

- Definition

Amount of any assets held either as collateral or by third parties that, upon the occurrence of any triggering event or condition under the guarantee, can be obtained and liquidated to recover all or a portion of the amounts paid under the guarantee.

+ References

No definition available.

+ Details

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X

- Definition

Guarantor Obligations, Production Tax Credits Sold

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

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

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- Definition

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.

+ References

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

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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