Name:	ale_LongTermContractForPurchaseOfElectricPowerAnticipatedDateOfNewTransmissionLine
Namespace Prefix:	ale_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

Long-Term Contract for Purchase of Electric Power, Date of Contract Expiration, Duration String

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerDateOfContractExpirationDurationString
Namespace Prefix:	ale_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

Date of approval by Minnesota Public Utilities Commission (MPUC) of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerDateOfMpucApproval
Namespace Prefix:	ale_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

The generating capacity of a production plant constructed and financed by a public utility district, cooperative, or other organization with whom exists a long-term contract to purchase electric power.

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerGeneratingUnitCapacityMw
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Number of long-term wind contracts to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerNumberOfWindPpas
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Share of plant output being purchased in megawatts under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerShareOfPlantOutputBeingPurchasedMw
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Share of plant output being purchased in megawatthours under a long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerShareOfPlantOutputBeingPurchasedMwh
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Start date of long-term contract to purchase electricity from a production plant constructed and financed by a public utility district, cooperative, or other organization.

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerStartDateOfContract
Namespace Prefix:	ale_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	duration

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.

No definition available.

Name:	ale_LongTermContractForPurchaseOfElectricPowerTermOfContractYears
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Capacity of a transmission line in kilovolts.

No definition available.

Name:	ale_TransmissionLineCapacityKv
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Date of purchase of a transmission line.

No definition available.

Name:	ale_TransmissionLinePurchaseDate
Namespace Prefix:	ale_
Data Type:	us-types:dateStringItemType
Balance Type:	na
Period Type:	instant

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section D

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-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=6499423&loc=d3e659339-123030

Name:	us-gaap_LongTermContractForPurchaseOfElectricPowerAmountOfLongTermDebtOrLeaseObligationOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service. If the utility is obligated to pay certain minimum amounts which cover debt service requirements whether or not the plant is operating, the amount can be disclosed here.

Name:	us-gaap_LongTermContractForPurchaseOfElectricPowerAnnualMinimumDebtServicePaymentRequired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

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.