Name:	ale_CommunityDevelopmentDistrictObligationAnnualAssessment
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Ownership percentage of property benefitied by a real estate development project funded by municipal capital improvement revenue and special assessment bonds.

No definition available.

Name:	ale_CommunityDevelopmentDistrictObligationOwnershipOfPropertyBenefited
Namespace Prefix:	ale_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Amount of any assets held either as collateral or by third parties that, upon the occurence 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.

No definition available.

Name:	ale_GuarantorObligationsCollateralHeldDirectlyorbyThirdPartiesAmount
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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.

No definition available.

Name:	us-gaap_GuaranteeObligationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

Name:	us-gaap_GuaranteeObligationsMaximumExposure
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Name:	ale_GuaranteeEntityandTypeAxis=ale_ALLETECleanEnergyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_FinancialStandbyLetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ale_GuaranteeEntityandTypeAxis=ale_U.S.WaterServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ale_GuaranteeEntityandTypeAxis=ale_BniCoalReclamationLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_SuretyBondMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ale_GuaranteeEntityandTypeAxis=ale_AlletePropertiesPerformanceAndMaintenanceObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_GuaranteeObligationsByNatureAxis=ale_SuretyBondsandLettersofCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ale_GuaranteeEntityandTypeAxis=ale_TownCenterCommunityDevelopmentDistrictMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: