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Commitments, Guarantees and Contingencies - North Dakota Wind Development (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2012 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 Wind Energy Center [Member] |
North Dakota Wind Development [Line Items] |
Generating Unit Capacity (MW) | 292
Bison 1 [Member] |
North Dakota Wind Development [Line Items] |
Transmission Line Length (Miles) | 22
Transmission Line Capacity (kV) | 230
Generating Unit Capacity (MW) | 82
Capital Cost Spent to Date | 174.9
Bison 2 [Member] |
North Dakota Wind Development [Line Items] |
Generating Unit Capacity (MW) | 105
Capital Cost Spent to Date | 148.6
Bison 3 [Member] |
North Dakota Wind Development [Line Items] |
Generating Unit Capacity (MW) | 105
Capital Cost Spent to Date | 149.8

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- Definition Capital cost spent to date for project. + References No definition available. + Details
Name: | ale_CapitalCostSpentToDate
Namespace Prefix: | ale_
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Balance Type: | debit
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- Definition Capacity of each generating unit/individual project in megawatts. + References No definition available. + Details
Name: | ale_GeneratingUnitCapacityMw
Namespace Prefix: | ale_
Data Type: | num:powerItemType
Balance Type: | na
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- Details
Name: | ale_NorthDakotaWindDevelopmentLineItems
Namespace Prefix: | ale_
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Period Type: | duration

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