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Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) (Manufactured Gas Plant Sites [Member], USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
Commitments and Contingencies [Line Items] |
Minimum range of estimated future costs | $ 14 lnt_MinimumRemainingEstimatedCostIncurredForInvestigationRemediationAndMonitoring
Maximum range of estimated future costs | 34 lnt_MaximumRemainingEstimatedCostIncurredForInvestigationRemediationAndMonitoring
Current and non-current environmental liabilities | 16 us-gaap_AccrualForEnvironmentalLossContingencies
IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum range of estimated future costs | 13 lnt_MinimumRemainingEstimatedCostIncurredForInvestigationRemediationAndMonitoring / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_NaturalGasProcessingPlantMember
Maximum range of estimated future costs | 31 lnt_MaximumRemainingEstimatedCostIncurredForInvestigationRemediationAndMonitoring / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_NaturalGasProcessingPlantMember
Current and non-current environmental liabilities | 14 us-gaap_AccrualForEnvironmentalLossContingencies / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_NaturalGasProcessingPlantMember
WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum range of estimated future costs | 1 lnt_MinimumRemainingEstimatedCostIncurredForInvestigationRemediationAndMonitoring / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_NaturalGasProcessingPlantMember
Maximum range of estimated future costs | 3 lnt_MaximumRemainingEstimatedCostIncurredForInvestigationRemediationAndMonitoring / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_NaturalGasProcessingPlantMember
Current and non-current environmental liabilities | $ 2 us-gaap_AccrualForEnvironmentalLossContingencies / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_NaturalGasProcessingPlantMember

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- Definition Maximum Remaining Estimated Cost Incurred for Investigation, Remediation and Monitoring + References No definition available. + Details
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- Definition Minimum Remaining Estimated Cost Incurred for Investigation, Remediation and Monitoring + References No definition available. + Details
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Balance Type: | debit
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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 + Details
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- Details
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- Details
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Period Type: |

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- Details
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Balance Type: |
Period Type: |