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Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Electric - generation [Member] | IPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 3.60%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricGenerationEquipmentMember | 3.60%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricGenerationEquipmentMember |  | 3.70%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricGenerationEquipmentMember
Electric - generation [Member] | WPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 3.20%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricGenerationEquipmentMember | 3.30%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricGenerationEquipmentMember | [1] | 3.20%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricGenerationEquipmentMember
Electric - distribution [Member] | IPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 2.50%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricDistributionMember | 2.50%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricDistributionMember |  | 2.50%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricDistributionMember
Electric - distribution [Member] | WPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 2.70%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricDistributionMember | 2.70%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricDistributionMember | [1] | 2.90%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_ElectricDistributionMember
Gas [Member] | IPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 3.30%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_GasTransmissionMember | 3.40%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_GasTransmissionMember |  | 3.40%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_GasTransmissionMember
Gas [Member] | WPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 2.50%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_GasTransmissionMember | 2.50%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_GasTransmissionMember | [1] | 2.60%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_GasTransmissionMember
Other [Member] | IPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 4.20%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_OtherPlantInServiceMember | 4.40%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_OtherPlantInServiceMember |  | 4.50%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_IplMember / us-gaap_PublicUtilityAxis = us-gaap_OtherPlantInServiceMember
Other [Member] | WPL [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Average rate of depreciation | 6.00%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_OtherPlantInServiceMember | 5.10%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_OtherPlantInServiceMember | [1] | 5.30%us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService / dei_LegalEntityAxis = lnt_WplMember / us-gaap_PublicUtilityAxis = us-gaap_OtherPlantInServiceMember
[1] | In 2012, the PSCW issued an order approving the implementation of updated depreciation rates for WPL effective January 1, 2013 as a result of a recently completed depreciation study. In 2013, the PSCW and FERC issued orders approving WPL’s requests to revise depreciation rates associated with the acquisition of Riverside effective January 1, 2013.

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- Definition Composite depreciation rate for public utility plants in service. + References No definition available. + Details
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