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Commitments, Guarantees and Contingencies - North Dakota Wind Development (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2011 Miles kV
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DC Transmission Line from Square Butte [Member] |
North Dakota Wind Development [Line Items] |
Transmission Line Length (Miles) | 465
Transmission Line Capacity (kV) | 250
Bison 1 Wind Project [Member] |
North Dakota Wind Development [Line Items] |
Generating Unit Capacity (MW) | 82
Expected Capital Cost | 177
Capital Cost Spent to Date | 171.5
MPUC, Current Cost Recovery, Approval Date | 2009
MPUC, Rates, Approval Date | July 2010
MPUC, Rates, Effective Date | August 1, 2010
MPUC Updated Approval Date | November 3, 2011
Bison 1 Wind Project, Phase 1 [Member] |
North Dakota Wind Development [Line Items] |
Transmission Line Length (Miles) | 22
Transmission Line Capacity (kV) | 230
Project Completion Date | 2010
Number of Turbines | 16
Capacity of Turbines (MW) | 2.3
Bison 1 Wind Project, Phase 2 [Member] |
North Dakota Wind Development [Line Items] |
Project Completion Date | January 2012
Number of Turbines | 15
Capacity of Turbines (MW) | 3.0
Bison 2 and 3 Wind Projects [Member] |
North Dakota Wind Development [Line Items] |
Generating Unit Capacity (MW) | 105
Project Completion Date | 2012
Expected Capital Cost | 160
Bison 2 Wind Project [Member] |
North Dakota Wind Development [Line Items] |
Capital Cost Spent to Date | 37.0
MPUC, Project, Approval Date | September 8, 2011
NDPSC, Site Permit, Approval Date | August 10, 2011
Bison 3 Wind Project [Member] |
North Dakota Wind Development [Line Items] |
Capital Cost Spent to Date | 14.7
MPUC, Project, Approval Date | November 2, 2011
NDPSC, Site Permit, Approval Date | October 12, 2011

X
- Definition Capacity of each turbine in megawatts at a site. + References No definition available. + Details
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X
- Definition Capital cost spent to date for project. + References No definition available. + Details
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Balance Type: | debit
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X
- Definition Expected capital cost for each individual project. + References No definition available. + Details
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Balance Type: | debit
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X
- Definition Capacity of each generating unit/individual project in megawatts. + References No definition available. + Details
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X
- Definition Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) of current cost recovery for expenditures and investments related to a project. + References No definition available. + Details
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Namespace Prefix: | ale_
Data Type: | us-types:dateStringItemType
Balance Type: | na
Period Type: | instant

X
- Definition Date/expected date of project approval by the Minnesota Public Utilities Commission (MPUC). + References No definition available. + Details
Name: | ale_MpucProjectApprovalDate
Namespace Prefix: | ale_
Data Type: | us-types:dateStringItemType
Balance Type: | na
Period Type: | instant

X
- Definition Date/expected date of approval by the Minnesota Public Utilities Commission (MPUC) establishing rates. + References No definition available. + Details
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Namespace Prefix: | ale_
Data Type: | us-types:dateStringItemType
Balance Type: | na
Period Type: | instant

X
- Definition Effective date of established rates as approved by the Minnesota Public Utilities Commission (MPUC). + References No definition available. + Details
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Namespace Prefix: | ale_
Data Type: | us-types:dateStringItemType
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Period Type: | instant

X
- Definition MPUCUpdatedApprovalDate + References No definition available. + Details
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Namespace Prefix: | ale_
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Balance Type: | na
Period Type: | instant

X
- Definition Date/expected date of approval of site permit by the North Dakota Public Service Commission (NDPSC). + References No definition available. + Details
Name: | ale_NdpscSitePermitApprovalDate
Namespace Prefix: | ale_
Data Type: | us-types:dateStringItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | ale_NorthDakotaWindDevelopmentLineItems
Namespace Prefix: | ale_
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X
- Definition Number of turbines at a site. + References No definition available. + Details
Name: | ale_NumberOfTurbines
Namespace Prefix: | ale_
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X
- Definition Date/expected date of project completion. + References No definition available. + Details
Name: | ale_ProjectCompletionDate
Namespace Prefix: | ale_
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Period Type: | instant

X
- Definition Capacity of a transmission line in kilovolts. + References No definition available. + Details
Name: | ale_TransmissionLineCapacityKv
Namespace Prefix: | ale_
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X
- Definition Length of a transmission line in miles. + References No definition available. + Details
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