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Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)	12 Months Ended
	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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