XML 49 R34.htm IDEA: XBRL DOCUMENT
v3.21.2

Regulatory Matters - Nemadji Trail Energy Center (Details) $ in Millions | 6 Months Ended
--- | ---
Jun. 30, 2021 USD ($) MW
Nemadji Trail Energy Center [Member] | Maximum [Member] |
Regulatory Matters [Line Items] |
Estimated Capital Expenditures, Including Past Expenditures | $ | $ 700
ALLETE, Inc. [Member] | Nemadji Trail Energy Center [Member] |
Regulatory Matters [Line Items] |
Estimated Capital Expenditures, Including Past Expenditures | $ | 350
ALLETE, Inc. [Member] | Nemadji Trail Energy Center [Member] | Maximum [Member] |
Regulatory Matters [Line Items] |
Total Project Costs Incurred to Date | $ | $ 15
MPUC [Member] | Resource Package [Member] | Natural Gas-fired [Member] | Combined-Cycle Natural Gas-Fired Generating Facility [Member] | Minimum [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Jointly Owned Electricity Generation Plant [Member] |
Regulatory Matters [Line Items] |
Generating Capacity to be Jointly Owned (MW) | MW | 525
MPUC [Member] | Resource Package [Member] | Natural Gas-fired [Member] | Combined-Cycle Natural Gas-Fired Generating Facility [Member] | Maximum [Member] | Jointly Owned by ALLETE and Dairyland Power Cooperative [Member] | Natural Gas PPA [Member] | Jointly Owned Electricity Generation Plant [Member] |
Regulatory Matters [Line Items] |
Generating Capacity to be Jointly Owned (MW) | MW | 550
MPUC [Member] | Resource Package [Member] | Minnesota Power [Member] | Natural Gas PPA [Member] |
Regulatory Matters [Line Items] |
Output Being Purchased (MW) | MW | 250
MPUC [Member] | Resource Package [Member] | Minnesota Power [Member] | Natural Gas-fired [Member] | Natural Gas PPA [Member] |
Regulatory Matters [Line Items] |
Expected Output Entitlement (Percent) | 50.00%

X
- Definition Capital cost spent to date for project. + References No definition available. + Details
Name: | ale_CapitalCostSpentToDate
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period. + References No definition available. + Details
Name: | ale_EstimatedCapitalExpendituresIncludingPastExpenditures
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Long-Term Contract for Purchase of Electric Power, Share of Plant Output Purchased + References No definition available. + Details
Name: | ale_LongTermContractForPurchaseOfElectricPowerShareOfPlantOutputPurchasedMw
Namespace Prefix: | ale_
Data Type: | dtr-types:powerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share of plant output being purchased under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.D) -URI http://asc.fasb.org/extlink&oid=122136240&loc=d3e659339-123030 + Details
Name: | us-gaap_LongTermContractForPurchaseOfElectricPowerShareOfPlantOutputBeingPurchased
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- 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 No definition available. + Details
Name: | us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ale_GeneratingFacilityAxisAxis=ale_NemadjiTrailEnergyCenterMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=ale_MPUCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilitiesRegulatoryProceedingAxis=ale_ResourcePackageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | ale_GeneratingFacilityAxisAxis=ale_CombinedCycleNaturalGasFiredGeneratingFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | us-gaap_JointlyOwnedUtilityPlantAxis=us-gaap_JointlyOwnedElectricityGenerationPlantMember
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: |