XML 56 R41.htm IDEA: XBRL DOCUMENT
v3.25.2

EQUITY INVESTMENTS - Narrative (Details) $ in Millions | 6 Months Ended
--- | ---
Jun. 30, 2025 USD ($) MW
Wind Turbine Generators | Tenaska | Tenaska PPA | Minnesota Power |
Investments In ATC [Roll Forward] |
Generating capacity counterparty owned (MegaWatt) | MW | 250
Long-term contract for purchase of electric power | 20 years
ATC |
Investments In ATC [Roll Forward] |
Ownership percentage | 8.00%
Basis point incentive adder | 0.50%
Approximate annual reduction in pretax income for FERC proposal to limit incentive adder, Allete's proportionate share | $ | $ 1
Nobles 2 |
Investments In ATC [Roll Forward] |
Ownership percentage | 49.00%

X
- Definition Approximate Annual Reduction In Pretax Income For FERC Proposal To Limit Incentive Adder, ALLETE's Proportionate Share + References No definition available. + Details
Name: | ale_ApproximateAnnualReductionInPretaxIncomeForFERCProposalToLimitIncentiveAdderALLETEsProportionateShare
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Basis Point Incentive Adder + References No definition available. + Details
Name: | ale_BasisPointIncentiveAdder
Namespace Prefix: | ale_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Generating Capacity Counterparty Owned (MW) + References No definition available. + Details
Name: | ale_GeneratingCapacityCounterpartyOwnedMW
Namespace Prefix: | ale_
Data Type: | dtr-types:powerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Investments In ATC + References No definition available. + Details
Name: | ale_InvestmentsInATCRollForward
Namespace Prefix: | ale_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Term in years of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. + References No definition available. + Details
Name: | ale_LongTermContractForPurchaseOfElectricPowerTermOfContractYears
Namespace Prefix: | ale_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 28 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-28 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 323 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481687/323-10-50-3 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | ale_GenerationTypeAxis=ale_WindTurbineGeneratorsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CounterpartyNameAxis=ale_TenaskaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermContractForPurchaseOfElectricPowerAxis=ale_TenaskaPPAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=ale_MinnesotaPowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ale_ATCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ale_Nobles2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |