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Investment in ATC - FERC Complaints (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
Sensitivity Analysis [Member] |
Sensitivity Analysis [Line Items] |
Basis Point Reduction on Approved Rate of Return on Common Equity | 50 ale_BasisPointReductiononApprovedRateofReturnonCommonEquity / ale_SensitivityAnalysisAxis = ale_SensitivityAnalysisMember
After-tax [Member] | Sensitivity Analysis [Member] |
Sensitivity Analysis [Line Items] |
Effect on Future Earnings, Amount | $ 0.5 us-gaap_EffectOnFutureEarningsAmount / ale_ExpensePresentationAxis = ale_AftertaxMember / ale_SensitivityAnalysisAxis = ale_SensitivityAnalysisMember
Pre-tax [Member] | Sensitivity Analysis [Member] |
Sensitivity Analysis [Line Items] |
Effect on Future Earnings, Amount | 0.9 us-gaap_EffectOnFutureEarningsAmount / ale_ExpensePresentationAxis = ale_PretaxMember / ale_SensitivityAnalysisAxis = ale_SensitivityAnalysisMember
FERC Complaint 1 [Member] |
Loss Contingencies [Line Items] |
Equity Method Investment, Proposed Return on Common Equity | 9.15%ale_EquityMethodInvestmentProposedReturnonCommonEquity / ale_FERCComplaintAxis = ale_FERCComplaint1Member
FERC Complaint 2 [Member] |
Loss Contingencies [Line Items] |
Equity Method Investment, Proposed Return on Common Equity | 8.67%ale_EquityMethodInvestmentProposedReturnonCommonEquity / ale_FERCComplaintAxis = ale_FERCComplaint2Member
Rainy River Energy [Member] |
Loss Contingencies [Line Items] |
Loss Contingency, Estimate of Possible Loss | 1.4 us-gaap_LossContingencyEstimateOfPossibleLoss / dei_LegalEntityAxis = ale_RainyRiverEnergyMember
Rainy River Energy [Member] | FERC Complaint 2 [Member] |
Loss Contingencies [Line Items] |
Loss Contingency, Estimate of Possible Loss | $ 1.1 us-gaap_LossContingencyEstimateOfPossibleLoss / ale_FERCComplaintAxis = ale_FERCComplaint2Member / dei_LegalEntityAxis = ale_RainyRiverEnergyMember

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- Definition A sensitivity analysis using basis point reduction. + References No definition available. + Details
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- Definition The proposed return on common equity, which would be dedicated to the utility plant in the investee accounted for under the equity method of accounting. + References No definition available. + Details
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- Details
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- Definition The quantified amount of the future effect on earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 + Details
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- Details
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- Definition Reflects the estimated amount of loss from the specified contingency as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
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- Details
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- Details
Name: | ale_ExpensePresentationAxis=ale_PretaxMember
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Period Type: |

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- Details
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Namespace Prefix: |
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- Details
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- Details
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- Details
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