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Regulated Operations - Conservation Improvement Program (Details) $ in Millions | Jun. 30, 2020 USD ($)
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Regulated Operations [Abstract] |
Conservation Improvement Program Goal, Next Fiscal Year | $ 10.5
Conservation Improvement Program Goal, In 2 Years | 10.7
Conservation Improvement Program Goal, In 3 Years | $ 10.9

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- Definition Conservation Improvement Program Goal, In 2 Years + References No definition available. + Details
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- Definition Conservation Improvement Program Goal, In 3 Years + References No definition available. + Details
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Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Conservation Improvement Program Goal, Next Fiscal Year + References No definition available. + Details
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Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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