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Regulatory Matters - Boswell Mercury Emissions Reduction Plan (Details) - Boswell Unit 4 [Member] $ in Millions | Jun. 30, 2015 USD ($)
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Schedule of Utility Generating Facilities [Line Items] |
Estimated Capital Expenditures | $ 260
Capital Expenditures to Date | $ 184

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- Definition Capital cost spent to date for project. + References No definition available. + Details
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Balance Type: | debit
Period Type: | instant

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- Definition The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period. + References No definition available. + Details
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Namespace Prefix: | ale_
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- Definition [Line Items] for Schedule of Generating Facilities owned by the Utility + References No definition available. + Details
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Namespace Prefix: | ale_
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Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
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Period Type: |