XML 50 R52.htm IDEA: XBRL DOCUMENT v2.4.1.9

Jointly-Owned Facilities and Projects (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Jointly-Owned Facilities and Projects [Line Items]
Plant in Service	$ 474.6us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService	$ 438.9us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService
Accumulated Depreciation	210.8us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation	198.5us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation
Construction Work in Progress	212.1us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress	129.2us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress
CapX2020 [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	3ale_NumberOfProjects / ale_TransmissionAxis = ale_Capx2020Member
Project in Progress [Member] | CapX2020 [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	1ale_NumberOfProjects / ale_ProjectStatusAxis = ale_ProjectinProgressMember / ale_TransmissionAxis = ale_Capx2020Member
Completed Project [Member] [Member] | CapX2020 [Member]
Jointly-Owned Facilities and Projects [Line Items]
Number of Projects	2ale_NumberOfProjects / ale_ProjectStatusAxis = ale_CompletedProjectMemberMember / ale_TransmissionAxis = ale_Capx2020Member
Boswell Unit 4 [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	80.00%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member	80.00%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member
Generating Capacity (MW)	585.0ale_GeneratingCapacityMw / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member
% Not Owned	20.00%ale_JointlyOwnedElectricFacilityPercentageNotOwned / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member
Plant in Service	419.1us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member	416.1us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member
Accumulated Depreciation	209.1us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member	197.5us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member
Construction Work in Progress	168.1us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member	71.5us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = ale_BoswellUnit4Member
CapX2020 Projects [Member]
Jointly-Owned Facilities and Projects [Line Items]
Plant in Service	55.5us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member	22.8us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member
Accumulated Depreciation	1.7us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member	1.0us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member
Construction Work in Progress	$ 44.0us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member	$ 57.7us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member
CapX2020 Projects [Member] | Minimum [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	9.30%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member / us-gaap_RangeAxis = us-gaap_MinimumMember	9.30%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member / us-gaap_RangeAxis = us-gaap_MinimumMember
CapX2020 Projects [Member] | Maximum [Member]
Jointly-Owned Facilities and Projects [Line Items]
% Ownership	14.70%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member / us-gaap_RangeAxis = us-gaap_MaximumMember	14.70%us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare / us-gaap_JointlyOwnedUtilityPlantAxis = ale_Capx2020Member / us-gaap_RangeAxis = us-gaap_MaximumMember

X

- Definition

Capacity of a generating facility, unit, or project in megawatts.

+ References

No definition available.

+ Details

Name:	ale_GeneratingCapacityMw
Namespace Prefix:	ale_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Jointly-Owned Electric Facility Percentage Not Owned

+ References

No definition available.

+ Details

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

X

- Definition

Number of projects.

+ References

No definition available.

+ Details

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

X

- Definition

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPlantInService
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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

X

- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfPlantAccumulatedDepreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	ale_ProjectStatusAxis=ale_CompletedProjectMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ale_ProjectStatusAxis=ale_ProjectinProgressMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ale_TransmissionAxis=ale_Capx2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=ale_BoswellUnit4Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_JointlyOwnedUtilityPlantAxis=ale_Capx2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: