00003525412020FYfalse000005248500001078320.010.01480,000,000480,000,000249,868,415245,022,800380,542381,23228.7326.241.521.421.342.502.5024,000,00024,000,00013,370,78813,370,7885.005.0018,000,00018,000,00013,236,60113,236,60116203.653.653.253.253.253.253.43.43.43.45.55.55.55.54.14.14.14.13.63.63.63.62.32.36.456.456.456.456.36.36.36.36.256.256.256.254.74.74.74.73.73.73.73.73.53.53.53.54.64.62.252.252.252.253.053.053.053.0533336.256.256.256.256.3756.3756.3756.3757.67.67.67.64.14.14.14.13.653.65123.453.453.753.751.44.254.255.065.061us-gaap:OtherLiabilitiesCurrentus-gaap:OtherLiabilitiesCurrentus-gaap:OtherLiabilitiesNoncurrentus-gaap:OtherLiabilitiesNoncurrent00003525412020-01-012020-12-310000352541lnt:IplMember2020-01-012020-12-310000352541lnt:WplMember2020-01-012020-12-31iso4217:USD00003525412020-06-300000352541lnt:IplMember2020-06-300000352541lnt:WplMember2020-06-30xbrli:shares00003525412021-01-310000352541lnt:IplMember2021-01-310000352541lnt:WplMember2021-01-310000352541us-gaap:FinanceReceivablesMemberlnt:IplMember2020-12-310000352541lnt:WplMember2020-12-3100003525412020-12-3100003525412019-01-012019-12-3100003525412018-01-012018-12-31iso4217:USDxbrli:shares00003525412019-12-3100003525412018-12-3100003525412017-12-310000352541us-gaap:CommonStockMember2017-12-310000352541us-gaap:AdditionalPaidInCapitalMember2017-12-310000352541us-gaap:RetainedEarningsMember2017-12-310000352541us-gaap:AccumulatedOtherComprehensiveIncomeMember2017-12-310000352541us-gaap:DeferredCompensationShareBasedPaymentsMember2017-12-310000352541us-gaap:PreferredStockMember2017-12-310000352541us-gaap:RetainedEarningsMember2018-01-012018-12-310000352541us-gaap:AdditionalPaidInCapitalMember2018-01-012018-12-310000352541us-gaap:DeferredCompensationShareBasedPaymentsMember2018-01-012018-12-310000352541us-gaap:AccumulatedOtherComprehensiveIncomeMember2018-01-012018-12-310000352541us-gaap:CommonStockMember2018-12-310000352541us-gaap:AdditionalPaidInCapitalMember2018-12-310000352541us-gaap:RetainedEarningsMember2018-12-310000352541us-gaap:AccumulatedOtherComprehensiveIncomeMember2018-12-310000352541us-gaap:DeferredCompensationShareBasedPaymentsMember2018-12-310000352541us-gaap:PreferredStockMember2018-12-310000352541us-gaap:RetainedEarningsMember2019-01-012019-12-310000352541us-gaap:AdditionalPaidInCapitalMember2019-01-012019-12-310000352541us-gaap:AccumulatedOtherComprehensiveIncomeMember2019-01-012019-12-310000352541us-gaap:CommonStockMember2019-12-310000352541us-gaap:AdditionalPaidInCapitalMember2019-12-310000352541us-gaap:RetainedEarningsMember2019-12-310000352541us-gaap:AccumulatedOtherComprehensiveIncomeMember2019-12-310000352541us-gaap:DeferredCompensationShareBasedPaymentsMember2019-12-310000352541us-gaap:PreferredStockMember2019-12-310000352541us-gaap:RetainedEarningsMember2020-01-012020-12-310000352541us-gaap:AdditionalPaidInCapitalMember2020-01-012020-12-310000352541us-gaap:DeferredCompensationShareBasedPaymentsMember2020-01-012020-12-310000352541us-gaap:RetainedEarningsMembersrt:CumulativeEffectPeriodOfAdoptionAdjustmentMember2019-12-310000352541srt:CumulativeEffectPeriodOfAdoptionAdjustmentMember2019-12-310000352541us-gaap:AccumulatedOtherComprehensiveIncomeMember2020-01-012020-12-310000352541us-gaap:CommonStockMember2020-12-310000352541us-gaap:AdditionalPaidInCapitalMember2020-12-310000352541us-gaap:RetainedEarningsMember2020-12-310000352541us-gaap:AccumulatedOtherComprehensiveIncomeMember2020-12-310000352541us-gaap:DeferredCompensationShareBasedPaymentsMember2020-12-310000352541us-gaap:PreferredStockMember2020-12-310000352541lnt:IplMember2020-12-310000352541lnt:IplMember2019-01-012019-12-310000352541lnt:IplMember2018-01-012018-12-310000352541lnt:IplMember2019-12-310000352541lnt:IplMember2018-12-310000352541lnt:IplMember2017-12-310000352541us-gaap:CommonStockMemberlnt:IplMember2017-12-310000352541lnt:IplMemberus-gaap:AdditionalPaidInCapitalMember2017-12-310000352541us-gaap:RetainedEarningsMemberlnt:IplMember2017-12-310000352541us-gaap:PreferredStockMemberlnt:IplMember2017-12-310000352541us-gaap:RetainedEarningsMemberlnt:IplMember2018-01-012018-12-310000352541lnt:IplMemberus-gaap:AdditionalPaidInCapitalMember2018-01-012018-12-310000352541us-gaap:CommonStockMemberlnt:IplMember2018-12-310000352541lnt:IplMemberus-gaap:AdditionalPaidInCapitalMember2018-12-310000352541us-gaap:RetainedEarningsMemberlnt:IplMember2018-12-310000352541us-gaap:PreferredStockMemberlnt:IplMember2018-12-310000352541us-gaap:RetainedEarningsMemberlnt:IplMember2019-01-012019-12-310000352541lnt:IplMemberus-gaap:AdditionalPaidInCapitalMember2019-01-012019-12-310000352541us-gaap:CommonStockMemberlnt:IplMember2019-12-310000352541lnt:IplMemberus-gaap:AdditionalPaidInCapitalMember2019-12-310000352541us-gaap:RetainedEarningsMemberlnt:IplMember2019-12-310000352541us-gaap:PreferredStockMemberlnt:IplMember2019-12-310000352541us-gaap:RetainedEarningsMemberlnt:IplMember2020-01-012020-12-310000352541lnt:IplMemberus-gaap:AdditionalPaidInCapitalMember2020-01-012020-12-310000352541us-gaap:CommonStockMemberlnt:IplMember2020-12-310000352541lnt:IplMemberus-gaap:AdditionalPaidInCapitalMember2020-12-310000352541us-gaap:RetainedEarningsMemberlnt:IplMember2020-12-310000352541us-gaap:PreferredStockMemberlnt:IplMember2020-12-310000352541lnt:WplMember2019-01-012019-12-310000352541lnt:WplMember2018-01-012018-12-310000352541lnt:WplMember2019-12-310000352541lnt:WplMember2018-12-310000352541lnt:WplMember2017-12-310000352541us-gaap:CommonStockMemberlnt:WplMember2017-12-310000352541us-gaap:AdditionalPaidInCapitalMemberlnt:WplMember2017-12-310000352541us-gaap:RetainedEarningsMemberlnt:WplMember2017-12-310000352541us-gaap:RetainedEarningsMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:AdditionalPaidInCapitalMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:CommonStockMemberlnt:WplMember2018-12-310000352541us-gaap:AdditionalPaidInCapitalMemberlnt:WplMember2018-12-310000352541us-gaap:RetainedEarningsMemberlnt:WplMember2018-12-310000352541us-gaap:RetainedEarningsMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:AdditionalPaidInCapitalMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:CommonStockMemberlnt:WplMember2019-12-310000352541us-gaap:AdditionalPaidInCapitalMemberlnt:WplMember2019-12-310000352541us-gaap:RetainedEarningsMemberlnt:WplMember2019-12-310000352541us-gaap:RetainedEarningsMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:AdditionalPaidInCapitalMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:CommonStockMemberlnt:WplMember2020-12-310000352541us-gaap:AdditionalPaidInCapitalMemberlnt:WplMember2020-12-310000352541us-gaap:RetainedEarningsMemberlnt:WplMember2020-12-31lnt:customerxbrli:pure0000352541lnt:AlliantEnergyFinanceLLCMember2020-12-31utr:MW0000352541lnt:AlliantEnergyFinanceLLCMember2020-01-012020-12-310000352541lnt:SheboyganFallsEnergyFacilityMember2020-01-012020-12-310000352541lnt:SheboyganFallsEnergyFacilityMember2020-12-310000352541us-gaap:ElectricGenerationEquipmentMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:ElectricGenerationEquipmentMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:ElectricGenerationEquipmentMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:ElectricGenerationEquipmentMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:ElectricGenerationEquipmentMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:ElectricGenerationEquipmentMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:ElectricDistributionMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:ElectricDistributionMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:ElectricDistributionMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:ElectricDistributionMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:ElectricDistributionMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:ElectricDistributionMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:OtherEnergyEquipmentMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:OtherEnergyEquipmentMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:OtherEnergyEquipmentMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:OtherEnergyEquipmentMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:OtherEnergyEquipmentMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:OtherEnergyEquipmentMemberlnt:WplMember2018-01-012018-12-310000352541lnt:IplMemberus-gaap:GasTransmissionMember2020-01-012020-12-310000352541lnt:IplMemberus-gaap:GasTransmissionMember2019-01-012019-12-310000352541lnt:IplMemberus-gaap:GasTransmissionMember2018-01-012018-12-310000352541us-gaap:GasTransmissionMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:GasTransmissionMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:GasTransmissionMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:WplMember2018-01-012018-12-310000352541lnt:IplMemberlnt:IPLfercformulawindgenerationMember2020-01-012020-12-310000352541lnt:IplMemberlnt:IPLfercformulawindgenerationMember2019-01-012019-12-310000352541lnt:IplMemberlnt:IPLfercformulawindgenerationMember2018-01-012018-12-310000352541lnt:IplMemberlnt:IplFercFormulaOtherProjectsMember2020-01-012020-12-310000352541lnt:IplMemberlnt:IplFercFormulaOtherProjectsMember2019-01-012019-12-310000352541lnt:IplMemberlnt:IplFercFormulaOtherProjectsMember2018-01-012018-12-310000352541lnt:WplPscwFormulaRetailJurisdictionMemberlnt:WplMember2020-01-012020-12-310000352541lnt:WplPscwFormulaRetailJurisdictionMemberlnt:WplMember2019-01-012019-12-310000352541lnt:WplPscwFormulaRetailJurisdictionMemberlnt:WplMember2018-01-012018-12-310000352541lnt:WplFercFormulaWholesaleJurisdictionMemberlnt:WplMember2020-01-012020-12-310000352541lnt:WplFercFormulaWholesaleJurisdictionMemberlnt:WplMember2019-01-012019-12-310000352541lnt:WplFercFormulaWholesaleJurisdictionMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:DeferredIncomeTaxChargesMember2020-12-310000352541us-gaap:DeferredIncomeTaxChargesMember2019-12-310000352541lnt:IplMemberus-gaap:DeferredIncomeTaxChargesMember2020-12-310000352541lnt:IplMemberus-gaap:DeferredIncomeTaxChargesMember2019-12-310000352541lnt:WplMemberus-gaap:DeferredIncomeTaxChargesMember2020-12-310000352541lnt:WplMemberus-gaap:DeferredIncomeTaxChargesMember2019-12-310000352541lnt:PensionAndOtherPostretirementBenefitsMember2020-12-310000352541lnt:PensionAndOtherPostretirementBenefitsMember2019-12-310000352541lnt:PensionAndOtherPostretirementBenefitsMemberlnt:IplMember2020-12-310000352541lnt:PensionAndOtherPostretirementBenefitsMemberlnt:IplMember2019-12-310000352541lnt:PensionAndOtherPostretirementBenefitsMemberlnt:WplMember2020-12-310000352541lnt:PensionAndOtherPostretirementBenefitsMemberlnt:WplMember2019-12-310000352541us-gaap:AssetRetirementObligationCostsMember2020-12-310000352541us-gaap:AssetRetirementObligationCostsMember2019-12-310000352541us-gaap:AssetRetirementObligationCostsMemberlnt:IplMember2020-12-310000352541us-gaap:AssetRetirementObligationCostsMemberlnt:IplMember2019-12-310000352541us-gaap:AssetRetirementObligationCostsMemberlnt:WplMember2020-12-310000352541us-gaap:AssetRetirementObligationCostsMemberlnt:WplMember2019-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMember2020-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMember2019-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:IplMember2020-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:IplMember2019-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:WplMember2020-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:WplMember2019-12-310000352541lnt:DAECPPAMember2020-12-310000352541lnt:DAECPPAMember2019-12-310000352541lnt:DAECPPAMemberlnt:IplMember2020-12-310000352541lnt:DAECPPAMemberlnt:IplMember2019-12-310000352541lnt:WesternWisconsinGasDistributionExpansionInvestmentsMember2020-12-310000352541lnt:WesternWisconsinGasDistributionExpansionInvestmentsMember2019-12-310000352541lnt:WesternWisconsinGasDistributionExpansionInvestmentsMemberlnt:WplMember2020-12-310000352541lnt:WesternWisconsinGasDistributionExpansionInvestmentsMemberlnt:WplMember2019-12-310000352541us-gaap:DeferredDerivativeGainLossMember2020-12-310000352541us-gaap:DeferredDerivativeGainLossMember2019-12-310000352541us-gaap:DeferredDerivativeGainLossMemberlnt:IplMember2020-12-310000352541us-gaap:DeferredDerivativeGainLossMemberlnt:IplMember2019-12-310000352541us-gaap:DeferredDerivativeGainLossMemberlnt:WplMember2020-12-310000352541us-gaap:DeferredDerivativeGainLossMemberlnt:WplMember2019-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMember2020-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMember2019-12-310000352541lnt:IplMemberus-gaap:OtherRegulatoryAssetsLiabilitiesMember2020-12-310000352541lnt:IplMemberus-gaap:OtherRegulatoryAssetsLiabilitiesMember2019-12-310000352541lnt:WplMemberus-gaap:OtherRegulatoryAssetsLiabilitiesMember2020-12-310000352541lnt:WplMemberus-gaap:OtherRegulatoryAssetsLiabilitiesMember2019-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:SutherlandUnitsOneAndThreeMemberlnt:IplMember2020-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:MLKappMemberlnt:IplMember2020-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:IplMemberlnt:AnalogElectricMetersMember2020-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:EdgewaterUnitThreeAndNelsonDeweyUnitsOneAndTwoMemberlnt:WplMember2020-12-310000352541lnt:ElectricGeneratingUnitsRetiredEarlyMemberMemberlnt:EdgewaterUnit4Memberlnt:WplMember2020-12-310000352541lnt:DAECPPAMember2020-09-012020-09-300000352541lnt:DAECPPAMember2020-01-012020-12-310000352541lnt:TaxRelatedMember2020-12-310000352541lnt:TaxRelatedMember2019-12-310000352541lnt:IplMemberlnt:TaxRelatedMember2020-12-310000352541lnt:IplMemberlnt:TaxRelatedMember2019-12-310000352541lnt:WplMemberlnt:TaxRelatedMember2020-12-310000352541lnt:WplMemberlnt:TaxRelatedMember2019-12-310000352541lnt:CostOfRemovalObligationsMember2020-12-310000352541lnt:CostOfRemovalObligationsMember2019-12-310000352541lnt:CostOfRemovalObligationsMemberlnt:IplMember2020-12-310000352541lnt:CostOfRemovalObligationsMemberlnt:IplMember2019-12-310000352541lnt:CostOfRemovalObligationsMemberlnt:WplMember2020-12-310000352541lnt:CostOfRemovalObligationsMemberlnt:WplMember2019-12-310000352541lnt:IplSElectricTransmissionServiceCostsMember2020-12-310000352541lnt:IplSElectricTransmissionServiceCostsMember2019-12-310000352541lnt:IplMemberlnt:IplSElectricTransmissionServiceCostsMember2020-12-310000352541lnt:IplMemberlnt:IplSElectricTransmissionServiceCostsMember2019-12-310000352541lnt:IplSElectricTransmissionServiceCostsMemberlnt:WplMember2020-12-310000352541lnt:IplSElectricTransmissionServiceCostsMemberlnt:WplMember2019-12-310000352541lnt:WestRiversideLiquidatedDamagesMember2020-12-310000352541lnt:WestRiversideLiquidatedDamagesMember2019-12-310000352541lnt:WestRiversideLiquidatedDamagesMemberlnt:WplMember2020-12-310000352541lnt:WestRiversideLiquidatedDamagesMemberlnt:WplMember2019-12-310000352541us-gaap:DeferredDerivativeGainLossMember2020-12-310000352541us-gaap:DeferredDerivativeGainLossMember2019-12-310000352541lnt:IplMemberus-gaap:DeferredDerivativeGainLossMember2020-12-310000352541lnt:IplMemberus-gaap:DeferredDerivativeGainLossMember2019-12-310000352541lnt:WplMemberus-gaap:DeferredDerivativeGainLossMember2020-12-310000352541lnt:WplMemberus-gaap:DeferredDerivativeGainLossMember2019-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMember2020-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMember2019-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMemberlnt:IplMember2020-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMemberlnt:IplMember2019-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMemberlnt:WplMember2020-12-310000352541us-gaap:OtherRegulatoryAssetsLiabilitiesMemberlnt:WplMember2019-12-310000352541lnt:IplMemberlnt:IplSElectricTransmissionServiceCostsMember2020-01-012020-12-310000352541lnt:DerechoWindstormMemberlnt:IplMember2020-08-012020-08-310000352541lnt:DerechoWindstormMemberlnt:IplMembersrt:ScenarioForecastMember2021-12-310000352541lnt:DerechoWindstormMemberlnt:IplMember2020-12-310000352541lnt:IplMemberlnt:TwoThousandTwentyTestPeriodRetailElectricMember2019-01-012019-12-310000352541lnt:IplMemberlnt:TwoThousandTwentyTestPeriodRetailElectricMember2020-01-012020-12-310000352541us-gaap:DeferredIncomeTaxChargesMemberlnt:IplMemberlnt:TwoThousandTwentyTestPeriodRetailElectricMember2020-12-310000352541lnt:IplMemberlnt:TwoThousandTwentyTestPeriodRetailElectricMemberus-gaap:RevenueSubjectToRefundMember2020-12-310000352541lnt:TwoThousandTwentyTestPeriodRetailGasMemberlnt:IplMember2020-01-012020-12-310000352541lnt:IplMemberlnt:TwoThousandSixteenTestYearRetailElectricMember2017-01-012017-12-310000352541lnt:IplMemberlnt:TwoThousandSixteenTestYearRetailElectricMember2018-01-012018-12-310000352541lnt:TwentyNineteenTestPeriodRetailElectricMemberlnt:WplMemberus-gaap:RevenueSubjectToRefundMember2020-01-012020-12-310000352541lnt:WplMemberlnt:TwoThousandTwentyTestPeriodRetailElectricMember2020-01-012020-12-310000352541lnt:ElectricGenerationMember2020-12-310000352541lnt:ElectricGenerationMember2019-12-310000352541lnt:ElectricGenerationMemberlnt:IplMember2020-12-310000352541lnt:ElectricGenerationMemberlnt:IplMember2019-12-310000352541lnt:ElectricGenerationMemberlnt:WplMember2020-12-310000352541lnt:ElectricGenerationMemberlnt:WplMember2019-12-310000352541us-gaap:ElectricDistributionMember2020-12-310000352541us-gaap:ElectricDistributionMember2019-12-310000352541us-gaap:ElectricDistributionMemberlnt:IplMember2020-12-310000352541us-gaap:ElectricDistributionMemberlnt:IplMember2019-12-310000352541us-gaap:ElectricDistributionMemberlnt:WplMember2020-12-310000352541us-gaap:ElectricDistributionMemberlnt:WplMember2019-12-310000352541us-gaap:OtherPlantInServiceMember2020-12-310000352541us-gaap:OtherPlantInServiceMember2019-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:IplMember2020-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:IplMember2019-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:WplMember2020-12-310000352541us-gaap:OtherPlantInServiceMemberlnt:WplMember2019-12-310000352541us-gaap:EquityMember2020-01-012020-12-310000352541us-gaap:EquityMember2019-01-012019-12-310000352541us-gaap:EquityMember2018-01-012018-12-310000352541lnt:IplMemberus-gaap:EquityMember2020-01-012020-12-310000352541lnt:IplMemberus-gaap:EquityMember2019-01-012019-12-310000352541lnt:IplMemberus-gaap:EquityMember2018-01-012018-12-310000352541us-gaap:EquityMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:EquityMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:EquityMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:DebtMember2020-01-012020-12-310000352541us-gaap:DebtMember2019-01-012019-12-310000352541us-gaap:DebtMember2018-01-012018-12-310000352541us-gaap:DebtMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:DebtMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:DebtMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:DebtMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:DebtMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:DebtMemberlnt:WplMember2018-01-012018-12-310000352541lnt:SheboyganFallsEnergyFacilityMember2020-01-012020-12-310000352541lnt:CustomerBillingAndInformationSystemMember2020-01-012020-12-310000352541us-gaap:SoftwareAndSoftwareDevelopmentCostsMember2020-01-012020-12-310000352541lnt:CorporateServicesMembersrt:MinimumMember2020-01-012020-12-310000352541srt:MaximumMemberlnt:CorporateServicesMember2020-01-012020-12-310000352541lnt:OttumwaUnit1Memberlnt:IplMember2020-12-310000352541lnt:GeorgeNealUnit4Memberlnt:IplMember2020-12-310000352541lnt:GeorgeNealUnit3Memberlnt:IplMember2020-12-310000352541lnt:IplMemberlnt:LouisaUnit1Member2020-12-310000352541lnt:ColumbiaUnits1And2Memberlnt:WplMember2020-12-310000352541lnt:RiversideEnergyCenterMemberlnt:WplMember2020-12-310000352541lnt:ForwardWindEnergyCenterMemberlnt:WplMember2020-12-310000352541srt:MaximumMember2020-12-310000352541lnt:IplMembersrt:MaximumMember2020-01-012020-12-310000352541lnt:IplMembersrt:MaximumMember2019-01-012019-12-310000352541lnt:IplMembersrt:MaximumMember2018-01-012018-12-310000352541srt:WeightedAverageMemberlnt:IplMember2020-01-012020-12-310000352541srt:WeightedAverageMemberlnt:IplMember2019-01-012019-12-310000352541srt:WeightedAverageMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:FinanceReceivablesMemberlnt:IplMember2019-12-310000352541lnt:InvestmentInAtcMember2020-12-310000352541lnt:InvestmentInAtcMember2019-12-310000352541lnt:InvestmentInAtcMember2020-01-012020-12-310000352541lnt:InvestmentInAtcMember2019-01-012019-12-310000352541lnt:InvestmentInAtcMember2018-01-012018-12-310000352541lnt:WindInvestmentinOklahomaMember2020-12-310000352541lnt:WindInvestmentinOklahomaMember2019-12-310000352541lnt:WindInvestmentinOklahomaMember2020-01-012020-12-310000352541lnt:WindInvestmentinOklahomaMember2019-01-012019-12-310000352541lnt:WindInvestmentinOklahomaMember2018-01-012018-12-310000352541lnt:OtherEquityMethodInvestmentsMember2020-12-310000352541lnt:OtherEquityMethodInvestmentsMember2019-12-310000352541lnt:OtherEquityMethodInvestmentsMember2020-01-012020-12-310000352541lnt:OtherEquityMethodInvestmentsMember2019-01-012019-12-310000352541lnt:OtherEquityMethodInvestmentsMember2018-01-012018-12-310000352541lnt:TotalsMember2020-12-310000352541lnt:TotalsMember2019-12-310000352541lnt:TotalsMember2020-01-012020-12-310000352541lnt:TotalsMember2019-01-012019-12-310000352541lnt:TotalsMember2018-01-012018-12-310000352541us-gaap:EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember2020-01-012020-12-310000352541us-gaap:EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember2019-01-012019-12-310000352541us-gaap:EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember2018-01-012018-12-310000352541us-gaap:EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember2020-12-310000352541us-gaap:EquityMethodInvestmentNonconsolidatedInvesteeOrGroupOfInvesteesMember2019-12-310000352541lnt:AmericanTransmissionCompanyLlcAtcMember2020-12-310000352541lnt:ATCHoldcoLLCMember2020-12-310000352541us-gaap:ForwardContractsMember2020-01-012020-12-310000352541us-gaap:ForwardContractsMember2019-01-012019-12-310000352541us-gaap:ForwardContractsMember2018-01-012018-12-310000352541lnt:AtTheMarketOfferingProgramMember2020-01-012020-12-310000352541lnt:AtTheMarketOfferingProgramMember2019-01-012019-12-310000352541lnt:AtTheMarketOfferingProgramMember2018-01-012018-12-310000352541us-gaap:ForwardContractsMember2019-12-310000352541us-gaap:ForwardContractsMember2020-12-310000352541us-gaap:RedeemablePreferredStockMemberlnt:IplMember2020-12-310000352541lnt:FivePointOnePercentageMemberus-gaap:RedeemablePreferredStockMemberlnt:IplMember2020-01-012020-12-310000352541lnt:FivePointOnePercentageMemberus-gaap:RedeemablePreferredStockMemberlnt:IplMember2019-01-012019-12-310000352541lnt:FivePointOnePercentageMemberus-gaap:RedeemablePreferredStockMemberlnt:IplMember2020-12-310000352541lnt:FivePointOnePercentageMemberus-gaap:RedeemablePreferredStockMemberlnt:IplMember2019-12-31lnt:board_memberlnt:Q0000352541srt:ParentCompanyMember2020-12-310000352541srt:ScenarioForecastMembersrt:ParentCompanyMember2021-12-310000352541lnt:IplMembersrt:ScenarioForecastMember2021-12-310000352541srt:ScenarioForecastMemberlnt:WplMember2021-12-310000352541lnt:ThreePointTwoFivePercentSeniorDebenturesDueTwoThousandTwentyFourMemberDomainlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointTwoFivePercentSeniorDebenturesDueTwoThousandTwentyFourMemberDomainlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointTwoFivePercentSeniorDebenturesDueTwoThousandTwentyFourMemberDomainlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointTwoFivePercentSeniorDebenturesDueTwoThousandTwentyFourMemberDomainlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointFourPercentSeniorDebenturesDueTwoThousandTwentyFiveMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointFourPercentSeniorDebenturesDueTwoThousandTwentyFiveMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointFourPercentSeniorDebenturesDueTwoThousandTwentyFiveMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointFourPercentSeniorDebenturesDueTwoThousandTwentyFiveMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SeniorDebenturesMemberlnt:FivePointFivePercentSeniorDebenturesDueTwoThousandTwentyFiveMember2020-12-310000352541lnt:IplMemberlnt:SeniorDebenturesMemberlnt:FivePointFivePercentSeniorDebenturesDueTwoThousandTwentyFiveMember2020-12-310000352541lnt:SeniorDebenturesMemberlnt:FivePointFivePercentSeniorDebenturesDueTwoThousandTwentyFiveMember2019-12-310000352541lnt:IplMemberlnt:SeniorDebenturesMemberlnt:FivePointFivePercentSeniorDebenturesDueTwoThousandTwentyFiveMember2019-12-310000352541lnt:FourPointOneSeniorDebenturesDueTwoThousandTwentyEightMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:FourPointOneSeniorDebenturesDueTwoThousandTwentyEightMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:FourPointOneSeniorDebenturesDueTwoThousandTwentyEightMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:FourPointOneSeniorDebenturesDueTwoThousandTwentyEightMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointSixPercentSeniorDebenturesDueTwoThousandTwentyNineMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointSixPercentSeniorDebenturesDueTwoThousandTwentyNineMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointSixPercentSeniorDebenturesDueTwoThousandTwentyNineMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointSixPercentSeniorDebenturesDueTwoThousandTwentyNineMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SeniorDebenturesMemberlnt:TwoPointThreePercentSeniorDebenturesDueTwoThousandThirtyMember2020-12-310000352541lnt:IplMemberlnt:SeniorDebenturesMemberlnt:TwoPointThreePercentSeniorDebenturesDueTwoThousandThirtyMember2020-12-310000352541lnt:SeniorDebenturesMemberlnt:TwoPointThreePercentSeniorDebenturesDueTwoThousandThirtyMember2019-12-310000352541lnt:IplMemberlnt:SeniorDebenturesMemberlnt:TwoPointThreePercentSeniorDebenturesDueTwoThousandThirtyMember2019-12-310000352541lnt:SixPointFourFivePercentSeniorDebenturesDueTwoThousandThirtyThreeMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:SixPointFourFivePercentSeniorDebenturesDueTwoThousandThirtyThreeMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:SixPointFourFivePercentSeniorDebenturesDueTwoThousandThirtyThreeMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SixPointFourFivePercentSeniorDebenturesDueTwoThousandThirtyThreeMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SixPointThreePercentSeniorDebenturesDueTwoThousandThirtyFourMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:SixPointThreePercentSeniorDebenturesDueTwoThousandThirtyFourMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:SixPointThreePercentSeniorDebenturesDueTwoThousandThirtyFourMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SixPointThreePercentSeniorDebenturesDueTwoThousandThirtyFourMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SixPointTwoFivePercentSeniorDebenturesDueTwoThousandThirtyNineMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:SixPointTwoFivePercentSeniorDebenturesDueTwoThousandThirtyNineMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:SixPointTwoFivePercentSeniorDebenturesDueTwoThousandThirtyNineMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SixPointTwoFivePercentSeniorDebenturesDueTwoThousandThirtyNineMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:FourPointSevenPercentSeniorDebenturesDueTwoThousandFortyThreeMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:FourPointSevenPercentSeniorDebenturesDueTwoThousandFortyThreeMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:FourPointSevenPercentSeniorDebenturesDueTwoThousandFortyThreeMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:FourPointSevenPercentSeniorDebenturesDueTwoThousandFortyThreeMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointSevenPercentSeniorDebenturesDueTwoThousandFortySixMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointSevenPercentSeniorDebenturesDueTwoThousandFortySixMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointSevenPercentSeniorDebenturesDueTwoThousandFortySixMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointSevenPercentSeniorDebenturesDueTwoThousandFortySixMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointFivePercentSeniorDebenturesDueTwoThousandFortyNineMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointFivePercentSeniorDebenturesDueTwoThousandFortyNineMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointFivePercentSeniorDebenturesDueTwoThousandFortyNineMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointFivePercentSeniorDebenturesDueTwoThousandFortyNineMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointSixFivePercentSeniorDebenturesDueTwoThousandTwentyMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointSixFivePercentSeniorDebenturesDueTwoThousandTwentyMemberlnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:ThreePointSixFivePercentSeniorDebenturesDueTwoThousandTwentyMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:ThreePointSixFivePercentSeniorDebenturesDueTwoThousandTwentyMemberlnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:SeniorDebenturesMember2020-12-310000352541lnt:IplMemberlnt:SeniorDebenturesMember2020-12-310000352541lnt:SeniorDebenturesMember2019-12-310000352541lnt:IplMemberlnt:SeniorDebenturesMember2019-12-310000352541lnt:DebenturesMemberlnt:TwoPointTwoFivePercentDebentureDueTwoThousandTwentyMember2020-12-310000352541lnt:DebenturesMemberlnt:TwoPointTwoFivePercentDebentureDueTwoThousandTwentyMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMemberlnt:TwoPointTwoFivePercentDebentureDueTwoThousandTwentyMember2019-12-310000352541lnt:DebenturesMemberlnt:TwoPointTwoFivePercentDebentureDueTwoThousandTwentyMemberlnt:WplMember2019-12-310000352541lnt:DebenturesMemberlnt:ThreePointZeroFiveDebentureDueTwoThousandAndTwentySevenMember2020-12-310000352541lnt:DebenturesMemberlnt:ThreePointZeroFiveDebentureDueTwoThousandAndTwentySevenMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMemberlnt:ThreePointZeroFiveDebentureDueTwoThousandAndTwentySevenMember2019-12-310000352541lnt:DebenturesMemberlnt:ThreePointZeroFiveDebentureDueTwoThousandAndTwentySevenMemberlnt:WplMember2019-12-310000352541lnt:DebenturesMemberlnt:ThreePercentDebenturesDueTwoThousandTwentyNineMember2020-12-310000352541lnt:DebenturesMemberlnt:ThreePercentDebenturesDueTwoThousandTwentyNineMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMemberlnt:ThreePercentDebenturesDueTwoThousandTwentyNineMember2019-12-310000352541lnt:DebenturesMemberlnt:ThreePercentDebenturesDueTwoThousandTwentyNineMemberlnt:WplMember2019-12-310000352541lnt:DebenturesMemberlnt:SixPointTwoFivePercentDebentureDueTwoThousandThirtyFourMember2020-12-310000352541lnt:DebenturesMemberlnt:WplMemberlnt:SixPointTwoFivePercentDebentureDueTwoThousandThirtyFourMember2020-12-310000352541lnt:DebenturesMemberlnt:SixPointTwoFivePercentDebentureDueTwoThousandThirtyFourMember2019-12-310000352541lnt:DebenturesMemberlnt:WplMemberlnt:SixPointTwoFivePercentDebentureDueTwoThousandThirtyFourMember2019-12-310000352541lnt:DebenturesMemberlnt:SixPointThreeSevenFivePercentDebentureDueTwoThousandThirtySevenMember2020-12-310000352541lnt:DebenturesMemberlnt:SixPointThreeSevenFivePercentDebentureDueTwoThousandThirtySevenMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMemberlnt:SixPointThreeSevenFivePercentDebentureDueTwoThousandThirtySevenMember2019-12-310000352541lnt:DebenturesMemberlnt:SixPointThreeSevenFivePercentDebentureDueTwoThousandThirtySevenMemberlnt:WplMember2019-12-310000352541lnt:DebenturesMemberlnt:SevenPointSixPercentDebentureDueTwoThousandThirtyEightMember2020-12-310000352541lnt:DebenturesMemberlnt:SevenPointSixPercentDebentureDueTwoThousandThirtyEightMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMemberlnt:SevenPointSixPercentDebentureDueTwoThousandThirtyEightMember2019-12-310000352541lnt:DebenturesMemberlnt:SevenPointSixPercentDebentureDueTwoThousandThirtyEightMemberlnt:WplMember2019-12-310000352541lnt:FourPointOnePercentDebentureDueTwoThousandFortyFourMemberMemberlnt:DebenturesMember2020-12-310000352541lnt:FourPointOnePercentDebentureDueTwoThousandFortyFourMemberMemberlnt:DebenturesMemberlnt:WplMember2020-12-310000352541lnt:FourPointOnePercentDebentureDueTwoThousandFortyFourMemberMemberlnt:DebenturesMember2019-12-310000352541lnt:FourPointOnePercentDebentureDueTwoThousandFortyFourMemberMemberlnt:DebenturesMemberlnt:WplMember2019-12-310000352541lnt:DebenturesMemberlnt:ThreePointSixFivePercentDebenturesDueTwoThousandFiftyMember2020-12-310000352541lnt:DebenturesMemberlnt:ThreePointSixFivePercentDebenturesDueTwoThousandFiftyMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMemberlnt:ThreePointSixFivePercentDebenturesDueTwoThousandFiftyMember2019-12-310000352541lnt:DebenturesMemberlnt:ThreePointSixFivePercentDebenturesDueTwoThousandFiftyMemberlnt:WplMember2019-12-310000352541lnt:DebenturesMemberlnt:FourPointSixPercentDebentureDueTwoThousandTwentyMember2020-12-310000352541lnt:DebenturesMemberlnt:FourPointSixPercentDebentureDueTwoThousandTwentyMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMemberlnt:FourPointSixPercentDebentureDueTwoThousandTwentyMember2019-12-310000352541lnt:DebenturesMemberlnt:FourPointSixPercentDebentureDueTwoThousandTwentyMemberlnt:WplMember2019-12-310000352541lnt:DebenturesMember2020-12-310000352541lnt:DebenturesMemberlnt:WplMember2020-12-310000352541lnt:DebenturesMember2019-12-310000352541lnt:DebenturesMemberlnt:WplMember2019-12-310000352541lnt:TermLoanCreditAgreementThroughMarchTwoThousandTwentyTwoMemberlnt:AlliantEnergyFinanceLLCMemberlnt:TermLoanCreditAgreementMember2020-12-310000352541lnt:TermLoanCreditAgreementThroughMarchTwoThousandTwentyTwoMemberlnt:AlliantEnergyFinanceLLCMemberlnt:TermLoanCreditAgreementMember2019-12-310000352541us-gaap:SeniorNotesMemberlnt:ThreePointFourFivePercentSeniorNotesDueTwoThousandTwentyTwoMemberlnt:CorporateServicesMember2020-12-310000352541us-gaap:SeniorNotesMemberlnt:ThreePointFourFivePercentSeniorNotesDueTwoThousandTwentyTwoMemberlnt:CorporateServicesMember2019-12-310000352541us-gaap:SeniorNotesMemberlnt:AlliantEnergyFinanceLLCMemberlnt:ThreepointsevenfiveseniornotesduetwothousandandtwentythreeMember2020-12-310000352541us-gaap:SeniorNotesMemberlnt:AlliantEnergyFinanceLLCMemberlnt:ThreepointsevenfiveseniornotesduetwothousandandtwentythreeMember2019-12-310000352541us-gaap:SeniorNotesMemberlnt:AlliantEnergyFinanceLLCMemberlnt:OnePointFourPercentSeniorNotesDueTwoThousandTwentySixMember2020-12-310000352541us-gaap:SeniorNotesMemberlnt:AlliantEnergyFinanceLLCMemberlnt:OnePointFourPercentSeniorNotesDueTwoThousandTwentySixMember2019-12-310000352541us-gaap:SeniorNotesMemberlnt:AlliantEnergyFinanceLLCMemberlnt:FourPointTwoFivePercentSeniorNotesDueTwoThousandAndTwentyEightMember2020-12-310000352541us-gaap:SeniorNotesMemberlnt:AlliantEnergyFinanceLLCMemberlnt:FourPointTwoFivePercentSeniorNotesDueTwoThousandAndTwentyEightMember2019-12-310000352541lnt:SheboyganPowerLlcMemberlnt:SeniorSecuredNotesMemberlnt:FivePointZeroSixPercentOtherSeniorNotesDueTwoThousandTwelveToTwoThousandTwentyFourMember2020-12-310000352541lnt:SheboyganPowerLlcMemberlnt:SeniorSecuredNotesMemberlnt:FivePointZeroSixPercentOtherSeniorNotesDueTwoThousandTwelveToTwoThousandTwentyFourMember2019-12-310000352541lnt:AlliantEnergyFinanceLLCMemberlnt:TermLoanCreditAgreementMemberlnt:TermLoanCreditAgreementThroughAprilTwoThousandandTwentyMember2020-12-310000352541lnt:AlliantEnergyFinanceLLCMemberlnt:TermLoanCreditAgreementMemberlnt:TermLoanCreditAgreementThroughAprilTwoThousandandTwentyMember2019-12-310000352541lnt:OnePercentAtDecemberThirtyFirstTwoThousandThirteenOtherLongTermDebtDueTwoThousandFourteenToTwoThousandTwentyFiveMemberlnt:OtherLongTermDebtMiscellaneousMember2020-12-310000352541lnt:OnePercentAtDecemberThirtyFirstTwoThousandThirteenOtherLongTermDebtDueTwoThousandFourteenToTwoThousandTwentyFiveMemberlnt:OtherLongTermDebtMiscellaneousMember2019-12-310000352541lnt:OtherLongTermDebtMember2020-12-310000352541lnt:OtherLongTermDebtMember2019-12-310000352541lnt:CorporateServicesMember2020-12-31lnt:lease_renewal_period_option0000352541lnt:WplMemberlnt:SheboyganFallsEnergyFacilityMember2020-01-012020-12-310000352541lnt:WplMemberlnt:SheboyganFallsEnergyFacilityMember2020-12-310000352541lnt:WplMemberlnt:SheboyganFallsEnergyFacilityMember2019-12-310000352541lnt:WplMemberlnt:SheboyganFallsEnergyFacilityMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:RetailResidentialMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:RetailResidentialMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:RetailResidentialMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailResidentialMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailResidentialMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailResidentialMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:RetailResidentialMemberlnt:WplMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:RetailResidentialMemberlnt:WplMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:RetailResidentialMemberlnt:WplMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:RetailCommercialMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:RetailCommercialMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:RetailCommercialMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailCommercialMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailCommercialMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailCommercialMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:RetailCommercialMemberlnt:WplMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:RetailCommercialMemberlnt:WplMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:RetailCommercialMemberlnt:WplMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:RetailIndustrialMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:RetailIndustrialMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:RetailIndustrialMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailIndustrialMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailIndustrialMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:IplMemberlnt:RetailIndustrialMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:WplMemberlnt:RetailIndustrialMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:WplMemberlnt:RetailIndustrialMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:WplMemberlnt:RetailIndustrialMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:WholesaleMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:WholesaleMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:WholesaleMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:WholesaleMemberlnt:IplMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:WholesaleMemberlnt:IplMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:WholesaleMemberlnt:IplMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:WholesaleMemberlnt:WplMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:WholesaleMemberlnt:WplMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:WholesaleMemberlnt:WplMember2018-01-012018-12-310000352541lnt:ElectricMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:ElectricMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:ElectricMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:IplMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:IplMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:IplMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:WplMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:WplMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:WplMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:ElectricMember2020-01-012020-12-310000352541lnt:ElectricMember2019-01-012019-12-310000352541lnt:ElectricMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:IplMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:IplMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:IplMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:WplMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:WplMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:WplMember2018-01-012018-12-310000352541lnt:RetailResidentialMemberlnt:GasMember2020-01-012020-12-310000352541lnt:RetailResidentialMemberlnt:GasMember2019-01-012019-12-310000352541lnt:RetailResidentialMemberlnt:GasMember2018-01-012018-12-310000352541lnt:IplMemberlnt:RetailResidentialMemberlnt:GasMember2020-01-012020-12-310000352541lnt:IplMemberlnt:RetailResidentialMemberlnt:GasMember2019-01-012019-12-310000352541lnt:IplMemberlnt:RetailResidentialMemberlnt:GasMember2018-01-012018-12-310000352541lnt:RetailResidentialMemberlnt:WplMemberlnt:GasMember2020-01-012020-12-310000352541lnt:RetailResidentialMemberlnt:WplMemberlnt:GasMember2019-01-012019-12-310000352541lnt:RetailResidentialMemberlnt:WplMemberlnt:GasMember2018-01-012018-12-310000352541lnt:RetailCommercialMemberlnt:GasMember2020-01-012020-12-310000352541lnt:RetailCommercialMemberlnt:GasMember2019-01-012019-12-310000352541lnt:RetailCommercialMemberlnt:GasMember2018-01-012018-12-310000352541lnt:IplMemberlnt:RetailCommercialMemberlnt:GasMember2020-01-012020-12-310000352541lnt:IplMemberlnt:RetailCommercialMemberlnt:GasMember2019-01-012019-12-310000352541lnt:IplMemberlnt:RetailCommercialMemberlnt:GasMember2018-01-012018-12-310000352541lnt:RetailCommercialMemberlnt:WplMemberlnt:GasMember2020-01-012020-12-310000352541lnt:RetailCommercialMemberlnt:WplMemberlnt:GasMember2019-01-012019-12-310000352541lnt:RetailCommercialMemberlnt:WplMemberlnt:GasMember2018-01-012018-12-310000352541lnt:GasMemberlnt:RetailIndustrialMember2020-01-012020-12-310000352541lnt:GasMemberlnt:RetailIndustrialMember2019-01-012019-12-310000352541lnt:GasMemberlnt:RetailIndustrialMember2018-01-012018-12-310000352541lnt:IplMemberlnt:GasMemberlnt:RetailIndustrialMember2020-01-012020-12-310000352541lnt:IplMemberlnt:GasMemberlnt:RetailIndustrialMember2019-01-012019-12-310000352541lnt:IplMemberlnt:GasMemberlnt:RetailIndustrialMember2018-01-012018-12-310000352541lnt:WplMemberlnt:GasMemberlnt:RetailIndustrialMember2020-01-012020-12-310000352541lnt:WplMemberlnt:GasMemberlnt:RetailIndustrialMember2019-01-012019-12-310000352541lnt:WplMemberlnt:GasMemberlnt:RetailIndustrialMember2018-01-012018-12-310000352541lnt:GasMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:GasMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:GasMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:IplMemberlnt:GasMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:IplMemberlnt:GasMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:IplMemberlnt:GasMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:WplMemberlnt:GasMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:WplMemberlnt:GasMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:WplMemberlnt:GasMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:GasMember2020-01-012020-12-310000352541lnt:GasMember2019-01-012019-12-310000352541lnt:GasMember2018-01-012018-12-310000352541lnt:IplMemberlnt:GasMember2020-01-012020-12-310000352541lnt:IplMemberlnt:GasMember2019-01-012019-12-310000352541lnt:IplMemberlnt:GasMember2018-01-012018-12-310000352541lnt:WplMemberlnt:GasMember2020-01-012020-12-310000352541lnt:WplMemberlnt:GasMember2019-01-012019-12-310000352541lnt:WplMemberlnt:GasMember2018-01-012018-12-310000352541lnt:SteamMemberlnt:OtherUtilityMember2020-01-012020-12-310000352541lnt:SteamMemberlnt:OtherUtilityMember2019-01-012019-12-310000352541lnt:SteamMemberlnt:OtherUtilityMember2018-01-012018-12-310000352541lnt:SteamMemberlnt:IplMemberlnt:OtherUtilityMember2020-01-012020-12-310000352541lnt:SteamMemberlnt:IplMemberlnt:OtherUtilityMember2019-01-012019-12-310000352541lnt:SteamMemberlnt:IplMemberlnt:OtherUtilityMember2018-01-012018-12-310000352541lnt:OtherUtilityMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:OtherUtilityMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:OtherUtilityMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:IplMemberlnt:OtherUtilityMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:IplMemberlnt:OtherUtilityMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:IplMemberlnt:OtherUtilityMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:WplMemberlnt:OtherUtilityMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541lnt:WplMemberlnt:OtherUtilityMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541lnt:WplMemberlnt:OtherUtilityMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541lnt:OtherUtilityMember2020-01-012020-12-310000352541lnt:OtherUtilityMember2019-01-012019-12-310000352541lnt:OtherUtilityMember2018-01-012018-12-310000352541lnt:IplMemberlnt:OtherUtilityMember2020-01-012020-12-310000352541lnt:IplMemberlnt:OtherUtilityMember2019-01-012019-12-310000352541lnt:IplMemberlnt:OtherUtilityMember2018-01-012018-12-310000352541lnt:WplMemberlnt:OtherUtilityMember2020-01-012020-12-310000352541lnt:WplMemberlnt:OtherUtilityMember2019-01-012019-12-310000352541lnt:WplMemberlnt:OtherUtilityMember2018-01-012018-12-310000352541us-gaap:AllOtherSegmentsMemberus-gaap:OtherCustomerMember2020-01-012020-12-310000352541us-gaap:AllOtherSegmentsMemberus-gaap:OtherCustomerMember2019-01-012019-12-310000352541us-gaap:AllOtherSegmentsMemberus-gaap:OtherCustomerMember2018-01-012018-12-310000352541us-gaap:AllOtherSegmentsMember2020-01-012020-12-310000352541us-gaap:AllOtherSegmentsMember2019-01-012019-12-310000352541us-gaap:AllOtherSegmentsMember2018-01-012018-12-310000352541lnt:IplSTaxBenefitRiderMember2020-01-012020-12-310000352541lnt:IplSTaxBenefitRiderMember2019-01-012019-12-310000352541lnt:IplSTaxBenefitRiderMember2018-01-012018-12-310000352541lnt:IplMemberlnt:IplSTaxBenefitRiderMember2020-01-012020-12-310000352541lnt:IplMemberlnt:IplSTaxBenefitRiderMember2019-01-012019-12-310000352541lnt:IplMemberlnt:IplSTaxBenefitRiderMember2018-01-012018-12-310000352541lnt:TaxBenefitRiderMember2020-01-012020-12-310000352541lnt:TaxBenefitRiderMember2019-01-012019-12-310000352541lnt:TaxBenefitRiderMember2018-01-012018-12-310000352541lnt:IplMemberlnt:TaxBenefitRiderMember2020-01-012020-12-310000352541lnt:IplMemberlnt:TaxBenefitRiderMember2019-01-012019-12-310000352541lnt:IplMemberlnt:TaxBenefitRiderMember2018-01-012018-12-310000352541us-gaap:DomesticCountryMember2020-12-310000352541us-gaap:DomesticCountryMemberlnt:IplMember2020-12-310000352541us-gaap:DomesticCountryMemberlnt:WplMember2020-12-310000352541us-gaap:StateAndLocalJurisdictionMember2020-12-310000352541lnt:IplMemberus-gaap:StateAndLocalJurisdictionMember2020-12-310000352541lnt:WplMemberus-gaap:StateAndLocalJurisdictionMember2020-12-310000352541lnt:IplMemberus-gaap:StateAndLocalJurisdictionMember2020-01-012020-12-310000352541us-gaap:StateAndLocalJurisdictionMember2020-01-012020-12-310000352541lnt:WplMemberus-gaap:StateAndLocalJurisdictionMember2020-01-012020-12-310000352541srt:ScenarioForecastMemberus-gaap:StateAndLocalJurisdictionMember2021-01-012021-12-310000352541lnt:IplMembersrt:ScenarioForecastMemberus-gaap:StateAndLocalJurisdictionMember2021-01-012021-12-310000352541srt:ScenarioForecastMemberlnt:WplMemberus-gaap:StateAndLocalJurisdictionMember2021-01-012021-12-310000352541us-gaap:PensionPlansDefinedBenefitMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMember2018-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2018-12-310000352541us-gaap:PensionPlansDefinedBenefitMember2020-01-012020-12-310000352541us-gaap:PensionPlansDefinedBenefitMember2019-01-012019-12-310000352541us-gaap:PensionPlansDefinedBenefitMember2018-01-012018-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2020-01-012020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2019-01-012019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMember2018-01-012018-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:MinimumMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:MaximumMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:MinimumMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:MaximumMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:MinimumMember2018-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:MaximumMember2018-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2018-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2018-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2018-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2018-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2018-01-012018-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:ScenarioForecastMember2021-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMembersrt:ScenarioForecastMember2021-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:ScenarioForecastMemberlnt:WplMember2021-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMembersrt:ScenarioForecastMember2021-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMembersrt:ScenarioForecastMember2021-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMembersrt:ScenarioForecastMemberlnt:WplMember2021-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:CashAndCashEquivalentsMembersrt:MinimumMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMembersrt:MaximumMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMembersrt:MinimumMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMembersrt:MaximumMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMembersrt:MinimumMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMembersrt:MaximumMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMembersrt:MinimumMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMembersrt:MaximumMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:RiskParitySecuritiesMembersrt:MinimumMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:RiskParitySecuritiesMembersrt:MaximumMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:RiskParitySecuritiesMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMembersrt:MinimumMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMembersrt:MaximumMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:CashAndCashEquivalentsMembersrt:MinimumMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMembersrt:MaximumMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMembersrt:MinimumMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMembersrt:MaximumMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMembersrt:MinimumMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMembersrt:MaximumMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:InternationalEquitySecuritiesMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMembersrt:MinimumMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMembersrt:MaximumMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FixedIncomeSecuritiesMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMember2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMember2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541lnt:AccruedInvestmentIncomeMemberus-gaap:PensionPlansDefinedBenefitMember2020-12-310000352541lnt:AccruedInvestmentIncomeMemberus-gaap:PensionPlansDefinedBenefitMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DefinedBenefitPlanDueToBrokersNetMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DefinedBenefitPlanDueToBrokersNetMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541lnt:GlobalAssetAllocationSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberlnt:WplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:PensionPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541us-gaap:PensionPlansDefinedBenefitMemberlnt:SubtotalMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:DomesticEquitySecuritiesMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:InternationalEquitySecuritiesMember2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541lnt:InternationalEquitySecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FixedIncomeSecuritiesMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Memberus-gaap:CashAndCashEquivalentsMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberlnt:WplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541us-gaap:FixedIncomeSecuritiesMemberus-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541us-gaap:OtherPostretirementBenefitPlansDefinedBenefitMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember2020-01-012020-12-310000352541lnt:OmnibusIncentivePlanMember2020-12-310000352541srt:MinimumMember2020-01-012020-12-310000352541srt:MaximumMember2020-01-012020-12-310000352541lnt:OmnibusIncentivePlanMember2020-01-012020-12-310000352541us-gaap:PerformanceSharesMember2020-01-012020-12-310000352541us-gaap:PerformanceSharesMembersrt:MinimumMember2020-01-012020-12-310000352541srt:MaximumMemberus-gaap:PerformanceSharesMember2020-01-012020-12-310000352541us-gaap:PerformanceSharesMember2019-12-310000352541us-gaap:PerformanceSharesMember2018-12-310000352541us-gaap:PerformanceSharesMember2019-01-012019-12-310000352541us-gaap:PerformanceSharesMember2020-12-310000352541lnt:PerformanceSharesAndUnitsMember2020-01-012020-12-310000352541lnt:PerformanceSharesLiabilityAwardsMember2019-12-310000352541lnt:PerformanceSharesLiabilityAwardsMember2018-12-310000352541lnt:PerformanceSharesLiabilityAwardsMember2017-12-310000352541lnt:PerformanceUnitsMember2019-12-310000352541lnt:PerformanceUnitsMember2018-12-310000352541lnt:PerformanceUnitsMember2017-12-310000352541lnt:PerformanceSharesLiabilityAwardsMember2020-01-012020-12-310000352541lnt:PerformanceSharesLiabilityAwardsMember2019-01-012019-12-310000352541lnt:PerformanceSharesLiabilityAwardsMember2018-01-012018-12-310000352541lnt:PerformanceUnitsMember2020-01-012020-12-310000352541lnt:PerformanceUnitsMember2019-01-012019-12-310000352541lnt:PerformanceUnitsMember2018-01-012018-12-310000352541lnt:PerformanceSharesLiabilityAwardsMember2020-12-310000352541lnt:PerformanceUnitsMember2020-12-310000352541lnt:PerformanceSharesAndUnitsMembersrt:MinimumMember2020-01-012020-12-310000352541lnt:PerformanceSharesAndUnitsMembersrt:MaximumMember2020-01-012020-12-310000352541lnt:TwoThousandEighteenGrantMemberlnt:PerformanceSharesLiabilityAwardsMember2020-12-310000352541lnt:PerformanceUnitsMemberlnt:TwoThousandEighteenGrantMember2020-12-310000352541lnt:TwoThousandEighteenGrantMemberlnt:PerformanceSharesLiabilityAwardsMember2020-01-012020-12-310000352541lnt:PerformanceUnitsMemberlnt:TwoThousandEighteenGrantMember2020-01-012020-12-310000352541lnt:TwoThousandSeventeenGrantMemberlnt:PerformanceSharesLiabilityAwardsMember2020-01-012020-12-310000352541lnt:TwoThousandSixteenGrantMemberlnt:PerformanceSharesLiabilityAwardsMember2019-01-012019-12-310000352541lnt:TwoThousandFifteenGrantMemberlnt:PerformanceSharesLiabilityAwardsMember2018-01-012018-12-310000352541lnt:PerformanceUnitsMemberlnt:TwoThousandSeventeenGrantMember2020-01-012020-12-310000352541lnt:TwoThousandSixteenGrantMemberlnt:PerformanceUnitsMember2019-01-012019-12-310000352541lnt:PerformanceUnitsMemberlnt:TwoThousandFifteenGrantMember2018-01-012018-12-310000352541us-gaap:RestrictedStockUnitsRSUMember2020-01-012020-12-310000352541us-gaap:RestrictedStockUnitsRSUMember2019-12-310000352541us-gaap:RestrictedStockUnitsRSUMember2018-12-310000352541us-gaap:RestrictedStockUnitsRSUMember2019-01-012019-12-310000352541us-gaap:RestrictedStockUnitsRSUMember2020-12-310000352541lnt:RestrictedStockUnitsLiabilityAwardsMember2020-01-012020-12-310000352541lnt:RestrictedStockUnitLiabilityAwardMember2020-01-012020-12-310000352541lnt:RestrictedStockUnitsLiabilityAwardsMember2019-12-310000352541lnt:RestrictedStockUnitsLiabilityAwardsMember2018-12-310000352541lnt:RestrictedStockUnitsLiabilityAwardsMember2017-12-310000352541lnt:RestrictedStockUnitsLiabilityAwardsMember2019-01-012019-12-310000352541lnt:RestrictedStockUnitsLiabilityAwardsMember2018-01-012018-12-310000352541lnt:RestrictedStockUnitsLiabilityAwardsMember2020-12-310000352541lnt:PerformanceRestrictedStockUnitMember2020-01-012020-12-310000352541lnt:PerformanceRestrictedStockUnitMembersrt:MinimumMember2020-01-012020-12-310000352541lnt:PerformanceRestrictedStockUnitMembersrt:MaximumMember2020-01-012020-12-310000352541lnt:PerformanceRestrictedStockUnitMember2019-12-310000352541lnt:PerformanceRestrictedStockUnitMember2018-12-310000352541lnt:PerformanceRestrictedStockUnitMember2017-12-310000352541lnt:PerformanceRestrictedStockUnitMember2019-01-012019-12-310000352541lnt:PerformanceRestrictedStockUnitMember2018-01-012018-12-310000352541lnt:PerformanceRestrictedStockUnitMember2020-12-31utr:MWh0000352541us-gaap:CommodityMemberlnt:FtrsMwhsMember2020-01-012020-12-31lnt:Dekatherms0000352541srt:NaturalGasPerThousandCubicFeetMemberus-gaap:CommodityMember2020-12-31utr:T0000352541us-gaap:CoalContractMemberus-gaap:CommodityMember2020-01-012020-12-31utr:gal0000352541srt:FuelMemberus-gaap:CommodityMember2020-01-012020-12-310000352541us-gaap:CommodityMemberlnt:IplMemberlnt:FtrsMwhsMember2020-01-012020-12-310000352541srt:NaturalGasPerThousandCubicFeetMemberus-gaap:CommodityMemberlnt:IplMember2020-12-310000352541us-gaap:CoalContractMemberus-gaap:CommodityMemberlnt:IplMember2020-01-012020-12-310000352541srt:FuelMemberus-gaap:CommodityMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:CommodityMemberlnt:WplMemberlnt:FtrsMwhsMember2020-01-012020-12-310000352541srt:NaturalGasPerThousandCubicFeetMemberus-gaap:CommodityMemberlnt:WplMember2020-12-310000352541us-gaap:CoalContractMemberus-gaap:CommodityMemberlnt:WplMember2020-01-012020-12-310000352541srt:FuelMemberus-gaap:CommodityMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:CommodityContractMember2020-12-310000352541us-gaap:CommodityContractMember2019-12-310000352541us-gaap:CommodityContractMemberlnt:IplMember2020-12-310000352541us-gaap:CommodityContractMemberlnt:IplMember2019-12-310000352541us-gaap:CommodityContractMemberlnt:WplMember2020-12-310000352541us-gaap:CommodityContractMemberlnt:WplMember2019-12-310000352541us-gaap:CarryingReportedAmountFairValueDisclosureMember2020-12-310000352541us-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:CarryingReportedAmountFairValueDisclosureMember2019-12-310000352541us-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:CarryingReportedAmountFairValueDisclosureMember2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:CarryingReportedAmountFairValueDisclosureMember2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541lnt:IplMemberus-gaap:CarryingReportedAmountFairValueDisclosureMember2020-12-310000352541lnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541lnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541lnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541lnt:IplMemberus-gaap:CarryingReportedAmountFairValueDisclosureMember2019-12-310000352541lnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541lnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541lnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:CarryingReportedAmountFairValueDisclosureMember2020-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2020-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2020-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2020-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:CarryingReportedAmountFairValueDisclosureMember2019-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:FairValueInputsLevel1Member2019-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:FairValueInputsLevel2Member2019-12-310000352541us-gaap:CommodityContractMemberlnt:IplMemberus-gaap:FairValueInputsLevel3Member2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:CarryingReportedAmountFairValueDisclosureMemberlnt:WplMember2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541us-gaap:CommodityContractMemberus-gaap:CarryingReportedAmountFairValueDisclosureMemberlnt:WplMember2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541us-gaap:CommodityContractMemberus-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541us-gaap:CarryingReportedAmountFairValueDisclosureMemberlnt:WplMember2020-12-310000352541us-gaap:FairValueInputsLevel1Memberlnt:WplMember2020-12-310000352541us-gaap:FairValueInputsLevel2Memberlnt:WplMember2020-12-310000352541us-gaap:FairValueInputsLevel3Memberlnt:WplMember2020-12-310000352541us-gaap:CarryingReportedAmountFairValueDisclosureMemberlnt:WplMember2019-12-310000352541us-gaap:FairValueInputsLevel1Memberlnt:WplMember2019-12-310000352541us-gaap:FairValueInputsLevel2Memberlnt:WplMember2019-12-310000352541us-gaap:FairValueInputsLevel3Memberlnt:WplMember2019-12-310000352541us-gaap:CommodityContractMember2019-12-310000352541us-gaap:CommodityContractMember2018-12-310000352541lnt:DeferredProceedsOfReceivablesSoldMember2019-12-310000352541lnt:DeferredProceedsOfReceivablesSoldMember2018-12-310000352541us-gaap:CommodityContractMember2020-01-012020-12-310000352541us-gaap:CommodityContractMember2019-01-012019-12-310000352541lnt:DeferredProceedsOfReceivablesSoldMember2020-01-012020-12-310000352541lnt:DeferredProceedsOfReceivablesSoldMember2019-01-012019-12-310000352541us-gaap:CommodityContractMember2020-12-310000352541lnt:DeferredProceedsOfReceivablesSoldMember2020-12-310000352541lnt:IplMemberus-gaap:CommodityContractMember2019-12-310000352541lnt:IplMemberus-gaap:CommodityContractMember2018-12-310000352541lnt:IplMemberlnt:DeferredProceedsOfReceivablesSoldMember2019-12-310000352541lnt:IplMemberlnt:DeferredProceedsOfReceivablesSoldMember2018-12-310000352541lnt:IplMemberus-gaap:CommodityContractMember2020-01-012020-12-310000352541lnt:IplMemberus-gaap:CommodityContractMember2019-01-012019-12-310000352541lnt:IplMemberlnt:DeferredProceedsOfReceivablesSoldMember2020-01-012020-12-310000352541lnt:IplMemberlnt:DeferredProceedsOfReceivablesSoldMember2019-01-012019-12-310000352541lnt:IplMemberus-gaap:CommodityContractMember2020-12-310000352541lnt:IplMemberlnt:DeferredProceedsOfReceivablesSoldMember2020-12-310000352541lnt:ExcludingFinancialTransmissionRightsMemberus-gaap:CommodityContractMember2020-12-310000352541lnt:FinancialTransmissionRightsMemberus-gaap:CommodityContractMember2020-12-310000352541lnt:ExcludingFinancialTransmissionRightsMemberlnt:IplMemberus-gaap:CommodityContractMember2020-12-310000352541lnt:FinancialTransmissionRightsMemberlnt:IplMemberus-gaap:CommodityContractMember2020-12-310000352541lnt:ExcludingFinancialTransmissionRightsMemberlnt:WplMemberus-gaap:CommodityContractMember2020-12-310000352541lnt:FinancialTransmissionRightsMemberlnt:WplMemberus-gaap:CommodityContractMember2020-12-310000352541lnt:ExcludingFinancialTransmissionRightsMemberus-gaap:CommodityContractMember2019-12-310000352541lnt:FinancialTransmissionRightsMemberus-gaap:CommodityContractMember2019-12-310000352541lnt:ExcludingFinancialTransmissionRightsMemberlnt:IplMemberus-gaap:CommodityContractMember2019-12-310000352541lnt:FinancialTransmissionRightsMemberlnt:IplMemberus-gaap:CommodityContractMember2019-12-310000352541lnt:ExcludingFinancialTransmissionRightsMemberlnt:WplMemberus-gaap:CommodityContractMember2019-12-310000352541lnt:FinancialTransmissionRightsMemberlnt:WplMemberus-gaap:CommodityContractMember2019-12-310000352541lnt:CapitalPurchaseObligationMember2020-01-012020-12-310000352541lnt:CapitalPurchaseObligationMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:PublicUtilitiesInventoryNaturalGasMember2020-12-310000352541us-gaap:CoalSupplyAgreementsMember2020-12-310000352541lnt:LongTermPurchaseCommitmentsOtherMember2020-12-310000352541lnt:IplMemberus-gaap:PublicUtilitiesInventoryNaturalGasMember2020-12-310000352541lnt:IplMemberus-gaap:CoalSupplyAgreementsMember2020-12-310000352541lnt:IplMemberlnt:LongTermPurchaseCommitmentsOtherMember2020-12-310000352541lnt:WplMemberus-gaap:PublicUtilitiesInventoryNaturalGasMember2020-12-310000352541us-gaap:CoalSupplyAgreementsMemberlnt:WplMember2020-12-310000352541lnt:WplMemberlnt:LongTermPurchaseCommitmentsOtherMember2020-12-310000352541lnt:WhitingPetroleumAffiliateMember2020-01-012020-12-310000352541lnt:WhitingPetroleumAffiliateMember2020-12-310000352541us-gaap:IndemnificationGuaranteeMember2020-12-310000352541us-gaap:IndemnificationGuaranteeMemberlnt:PurchasedPowerMember2020-12-310000352541srt:MinimumMemberus-gaap:NaturalGasProcessingPlantMember2020-01-012020-12-310000352541srt:MaximumMemberus-gaap:NaturalGasProcessingPlantMember2020-01-012020-12-310000352541lnt:IplMembersrt:MinimumMemberus-gaap:NaturalGasProcessingPlantMember2020-01-012020-12-310000352541lnt:IplMembersrt:MaximumMemberus-gaap:NaturalGasProcessingPlantMember2020-01-012020-12-310000352541us-gaap:NaturalGasProcessingPlantMember2020-12-310000352541lnt:IplMemberus-gaap:NaturalGasProcessingPlantMember2020-12-310000352541lnt:FederalEnergyRegulatoryCommissionMember2019-01-012019-12-310000352541lnt:FederalEnergyRegulatoryCommissionMember2017-01-012017-12-310000352541lnt:FederalEnergyRegulatoryCommissionMemberlnt:IplMember2020-01-012020-12-310000352541lnt:FederalEnergyRegulatoryCommissionMemberlnt:WplMember2020-01-012020-12-31lnt:segment0000352541lnt:UtilityBusinessMember2020-01-012020-12-310000352541lnt:UtilityBusinessMember2020-01-012020-12-310000352541us-gaap:UnregulatedOperationMember2020-01-012020-12-310000352541lnt:ElectricMember2020-12-310000352541lnt:GasMember2020-12-310000352541lnt:OtherUtilityMember2020-12-310000352541lnt:UtilityBusinessMember2020-12-310000352541us-gaap:UnregulatedOperationMember2020-12-310000352541lnt:UtilityBusinessMember2019-01-012019-12-310000352541us-gaap:UnregulatedOperationMember2019-01-012019-12-310000352541lnt:ElectricMember2019-12-310000352541lnt:GasMember2019-12-310000352541lnt:OtherUtilityMember2019-12-310000352541lnt:UtilityBusinessMember2019-12-310000352541us-gaap:UnregulatedOperationMember2019-12-310000352541lnt:UtilityBusinessMember2018-01-012018-12-310000352541us-gaap:UnregulatedOperationMember2018-01-012018-12-310000352541lnt:ElectricMember2018-12-310000352541lnt:GasMember2018-12-310000352541lnt:OtherUtilityMember2018-12-310000352541lnt:UtilityBusinessMember2018-12-310000352541us-gaap:UnregulatedOperationMember2018-12-310000352541lnt:IplMemberlnt:UtilityBusinessMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:IplMember2020-12-310000352541lnt:IplMemberlnt:GasMember2020-12-310000352541lnt:IplMemberlnt:OtherUtilityMember2020-12-310000352541lnt:IplMemberlnt:UtilityBusinessMember2020-12-310000352541lnt:IplMemberlnt:UtilityBusinessMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:IplMember2019-12-310000352541lnt:IplMemberlnt:GasMember2019-12-310000352541lnt:IplMemberlnt:OtherUtilityMember2019-12-310000352541lnt:IplMemberlnt:UtilityBusinessMember2019-12-310000352541lnt:IplMemberlnt:UtilityBusinessMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:IplMember2018-12-310000352541lnt:IplMemberlnt:GasMember2018-12-310000352541lnt:IplMemberlnt:OtherUtilityMember2018-12-310000352541lnt:IplMemberlnt:UtilityBusinessMember2018-12-310000352541lnt:WplMemberlnt:UtilityBusinessMember2020-01-012020-12-310000352541lnt:ElectricMemberlnt:WplMember2020-12-310000352541lnt:WplMemberlnt:GasMember2020-12-310000352541lnt:WplMemberlnt:OtherUtilityMember2020-12-310000352541lnt:WplMemberlnt:UtilityBusinessMember2020-12-310000352541lnt:WplMemberlnt:UtilityBusinessMember2019-01-012019-12-310000352541lnt:ElectricMemberlnt:WplMember2019-12-310000352541lnt:WplMemberlnt:GasMember2019-12-310000352541lnt:WplMemberlnt:OtherUtilityMember2019-12-310000352541lnt:WplMemberlnt:UtilityBusinessMember2019-12-310000352541lnt:WplMemberlnt:UtilityBusinessMember2018-01-012018-12-310000352541lnt:ElectricMemberlnt:WplMember2018-12-310000352541lnt:WplMemberlnt:GasMember2018-12-310000352541lnt:WplMemberlnt:OtherUtilityMember2018-12-310000352541lnt:WplMemberlnt:UtilityBusinessMember2018-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:AdministrativeandGeneralServicesBillingsMemberlnt:IplMemberlnt:CorporateServicesMember2020-01-012020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:AdministrativeandGeneralServicesBillingsMemberlnt:IplMemberlnt:CorporateServicesMember2019-01-012019-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:AdministrativeandGeneralServicesBillingsMemberlnt:IplMemberlnt:CorporateServicesMember2018-01-012018-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:AdministrativeandGeneralServicesBillingsMemberlnt:WplMemberlnt:CorporateServicesMember2020-01-012020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:AdministrativeandGeneralServicesBillingsMemberlnt:WplMemberlnt:CorporateServicesMember2019-01-012019-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:AdministrativeandGeneralServicesBillingsMemberlnt:WplMemberlnt:CorporateServicesMember2018-01-012018-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:IplMemberlnt:TransmissionSalesCreditedMemberlnt:CorporateServicesMember2020-01-012020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:IplMemberlnt:TransmissionSalesCreditedMemberlnt:CorporateServicesMember2019-01-012019-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:IplMemberlnt:TransmissionSalesCreditedMemberlnt:CorporateServicesMember2018-01-012018-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:WplMemberlnt:TransmissionSalesCreditedMemberlnt:CorporateServicesMember2020-01-012020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:WplMemberlnt:TransmissionSalesCreditedMemberlnt:CorporateServicesMember2019-01-012019-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:WplMemberlnt:TransmissionSalesCreditedMemberlnt:CorporateServicesMember2018-01-012018-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:TransmissionPurchasesBilledMemberlnt:IplMemberlnt:CorporateServicesMember2020-01-012020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:TransmissionPurchasesBilledMemberlnt:IplMemberlnt:CorporateServicesMember2019-01-012019-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:TransmissionPurchasesBilledMemberlnt:IplMemberlnt:CorporateServicesMember2018-01-012018-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:TransmissionPurchasesBilledMemberlnt:WplMemberlnt:CorporateServicesMember2020-01-012020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:TransmissionPurchasesBilledMemberlnt:WplMemberlnt:CorporateServicesMember2019-01-012019-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:TransmissionPurchasesBilledMemberlnt:WplMemberlnt:CorporateServicesMember2018-01-012018-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:IplMemberlnt:CorporateServicesMember2020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:IplMemberlnt:CorporateServicesMember2019-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:WplMemberlnt:CorporateServicesMember2020-12-310000352541us-gaap:SubsidiaryOfCommonParentMemberlnt:WplMemberlnt:CorporateServicesMember2019-12-310000352541lnt:AtcBillingsToWplMemberlnt:WplMemberlnt:AmericanTransmissionCompanyLlcAtcMemberus-gaap:EquityMethodInvestmentsMember2020-01-012020-12-310000352541lnt:AtcBillingsToWplMemberlnt:WplMemberlnt:AmericanTransmissionCompanyLlcAtcMemberus-gaap:EquityMethodInvestmentsMember2019-01-012019-12-310000352541lnt:AtcBillingsToWplMemberlnt:WplMemberlnt:AmericanTransmissionCompanyLlcAtcMemberus-gaap:EquityMethodInvestmentsMember2018-01-012018-12-310000352541lnt:WplBillingsToAtcMemberlnt:WplMemberlnt:AmericanTransmissionCompanyLlcAtcMemberus-gaap:EquityMethodInvestmentsMember2020-01-012020-12-310000352541lnt:WplBillingsToAtcMemberlnt:WplMemberlnt:AmericanTransmissionCompanyLlcAtcMemberus-gaap:EquityMethodInvestmentsMember2019-01-012019-12-310000352541lnt:WplBillingsToAtcMemberlnt:WplMemberlnt:AmericanTransmissionCompanyLlcAtcMemberus-gaap:EquityMethodInvestmentsMember2018-01-012018-12-310000352541lnt:WplOwedAtcMemberlnt:WplMember2020-12-310000352541lnt:WplOwedAtcMemberlnt:WplMember2019-12-310000352541srt:ParentCompanyMember2020-01-012020-12-310000352541srt:ParentCompanyMember2019-01-012019-12-310000352541srt:ParentCompanyMember2018-01-012018-12-310000352541srt:ParentCompanyMember2019-12-310000352541srt:ParentCompanyMember2018-12-310000352541srt:ParentCompanyMember2017-12-310000352541us-gaap:AllowanceForCreditLossMember2019-12-310000352541us-gaap:AllowanceForCreditLossMember2020-01-012020-12-310000352541us-gaap:AllowanceForCreditLossMember2020-12-310000352541us-gaap:AllowanceForCreditLossMember2018-12-310000352541us-gaap:AllowanceForCreditLossMember2019-01-012019-12-310000352541us-gaap:AllowanceForCreditLossMember2017-12-310000352541us-gaap:AllowanceForCreditLossMember2018-01-012018-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:IplMember2019-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:IplMember2020-01-012020-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:IplMember2020-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:IplMember2018-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:IplMember2019-01-012019-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:IplMember2017-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:IplMember2018-01-012018-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:WplMember2019-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:WplMember2020-01-012020-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:WplMember2020-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:WplMember2018-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:WplMember2019-01-012019-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:WplMember2017-12-310000352541us-gaap:AllowanceForCreditLossMemberlnt:WplMember2018-01-012018-12-31
Table of Contents
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549
FORM 10-K
    ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the fiscal year ended December 31, 2020

or

    TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the transition period from                    to                    

lnt-20201231_g1.jpg
Name of Registrant, State of Incorporation, Address of Principal Executive Offices, Telephone Number, Commission File Number, IRS Employer Identification Number

ALLIANT ENERGY CORPORATION
(a Wisconsin Corporation)
4902 N. Biltmore Lane
Madison, Wisconsin 53718
Telephone (608) 458-3311
Commission File Number - 1-9894
IRS Employer Identification Number - 39-1380265

INTERSTATE POWER & LIGHT COMPANY
(an Iowa corporation)
Alliant Energy Tower
Cedar Rapids, Iowa 52401
Telephone (319) 786-4411
Commission File Number - 1-4117
IRS Employer Identification Number - 42-0331370

WISCONSIN POWER & LIGHT COMPANY
(a Wisconsin corporation)
4902 N. Biltmore Lane
Madison, Wisconsin 53718
Telephone (608) 458-3311
Commission File Number - 0-337
IRS Employer Identification Number - 39-0714890
This combined Form 10-K is separately filed by Alliant Energy Corporation, Interstate Power and Light Company and Wisconsin Power and Light Company. Information contained in the Form 10-K relating to Interstate Power and Light Company and Wisconsin Power and Light Company is filed by each such registrant on its own behalf. Each of Interstate Power and Light Company and Wisconsin Power and Light Company makes no representation as to information relating to registrants other than itself.

Securities registered pursuant to Section 12(b) of the Act:
Alliant Energy Corporation, Common Stock, $0.01 Par Value, Trading Symbol LNT, Nasdaq Global Select Market
Interstate Power and Light Company, 5.100% Series D Cumulative Perpetual Preferred Stock, $0.01 Par Value, Trading Symbol IPLDP, Nasdaq Global Select Market

Securities registered pursuant to Section 12(g) of the Act: None
Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.
Alliant Energy Corporation - Yes ☒ No ☐
Interstate Power and Light Company - Yes ☒ No ☐
Wisconsin Power and Light Company - Yes ☒ No ☐
Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.
Alliant Energy Corporation - Yes ☐ No
Interstate Power and Light Company - Yes ☐ No
Wisconsin Power and Light Company - Yes ☐ No
Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrants were required to file such reports) and (2) has been subject to such filing requirements for the past 90 days.
Alliant Energy Corporation - Yes ☒ No ☐
Interstate Power and Light Company - Yes ☒ No ☐
Wisconsin Power and Light Company - Yes ☒ No ☐
Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).
Alliant Energy Corporation - Yes ☒ No ☐
Interstate Power and Light Company - Yes ☒ No ☐
Wisconsin Power and Light Company - Yes ☒ No ☐
Indicate by check mark whether the registrant is a large accelerated filer, accelerated filer, non-accelerated filer, smaller reporting company, or emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.
Alliant Energy Corporation - Large Accelerated Filer ☒ Accelerated Filer ☐ Non-accelerated Filer ☐ Smaller Reporting Company Emerging Growth Company
Interstate Power and Light Company - Large Accelerated Filer ☐ Accelerated Filer ☐ Non-accelerated Filer ☒ Smaller Reporting Company Emerging Growth Company
Wisconsin Power and Light Company - Large Accelerated Filer ☐ Accelerated Filer ☐ Non-accelerated Filer ☒ Smaller Reporting Company Emerging Growth Company
If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.
Alliant Energy Corporation ☐
Interstate Power and Light Company ☐
Wisconsin Power and Light Company ☐
Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (§ 15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report.
Alliant Energy Corporation
Interstate Power and Light Company ☐
Wisconsin Power and Light Company ☐
Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).
Alliant Energy Corporation - Yes No ☒
Interstate Power and Light Company - Yes No ☒
Wisconsin Power and Light Company - Yes No ☒
The aggregate market value of the voting and non-voting common equity held by nonaffiliates as of June 30, 2020:
Alliant Energy Corporation - $11.9 billion
Interstate Power and Light Company - $0
Wisconsin Power and Light Company - $0
Number of shares outstanding of each class of common stock as of January 31, 2021:
Alliant Energy Corporation, Common Stock, $0.01 par value, 249,881,050 shares outstanding
Interstate Power and Light Company, Common Stock, $2.50 par value, 13,370,788 shares outstanding (all outstanding shares are owned beneficially and of record by Alliant Energy Corporation)
Wisconsin Power and Light Company, Common Stock, $5 par value, 13,236,601 shares outstanding (all outstanding shares are owned beneficially and of record by Alliant Energy Corporation)
DOCUMENTS INCORPORATED BY REFERENCE
Portions of the Proxy Statement relating to Alliant Energy Corporation’s 2021 Annual Meeting of Shareowners are, or will be upon filing with the Securities and Exchange Commission, incorporated by reference into Part III hereof.


Table of Contents
TABLE OF CONTENTS
Page Number
10. Leases



Table of Contents
DEFINITIONS
The following abbreviations or acronyms used in this report are defined below:
Abbreviation or AcronymDefinitionAbbreviation or AcronymDefinition
2021 Alliant Energy Proxy StatementAlliant Energy’s Proxy Statement for the 2021 Annual Meeting of ShareownersFuel-relatedElectric production fuel and purchased power
AEFAlliant Energy Finance, LLCGAAPU.S. generally accepted accounting principles
AFUDCAllowance for funds used during constructionGHGGreenhouse gases
Alliant EnergyAlliant Energy CorporationIPLInterstate Power and Light Company
AROAsset retirement obligationIRSInternal Revenue Service
ATCAmerican Transmission Company LLCITCITC Midwest LLC
ATC HoldingsInterest in American Transmission Company LLC and ATC Holdco LLCIUBIowa Utilities Board
ATIAE Transco Investments, LLCKWhKilowatt-hour
CACertificate of authorityMarshalltownMarshalltown Generating Station
CAAClean Air ActMDAManagement’s Discussion and Analysis of Financial Condition and Results of Operations
CCRCoal combustion residualsMGPManufactured gas plant
CO2Carbon dioxideMISOMidcontinent Independent System Operator, Inc.
Corporate ServicesAlliant Energy Corporate Services, Inc.MWMegawatt
COVID-19Novel coronavirusMWhMegawatt-hour
CPCNCertificate of Public Convenience and NecessityN/ANot applicable
CWIPConstruction work in progressNote(s)Combined Notes to Consolidated Financial Statements
DAECDuane Arnold Energy CenterOIPAlliant Energy Omnibus Incentive Plan
DCPAlliant Energy Deferred Compensation PlanOPEBOther postretirement benefits
DLIPAlliant Energy Director Long Term Incentive PlanPPAPurchased power agreement
DthDekathermPSCWPublic Service Commission of Wisconsin
EEPEnergy efficiency planReceivables AgreementReceivables Purchase and Sale Agreement
EGUElectric generating unitRiversideRiverside Energy Center
EPAU.S. Environmental Protection AgencySECSecurities and Exchange Commission
EPSEarnings per weighted average common shareU.S.United States of America
Federal Tax ReformTax Cuts and Jobs ActVEBAVoluntary Employees’ Beneficiary Association
FERCFederal Energy Regulatory CommissionVIEVariable interest entity
Financial StatementsConsolidated Financial StatementsWhiting PetroleumWhiting Petroleum Corporation
FTRFinancial transmission rightWPLWisconsin Power and Light Company

FORWARD-LOOKING STATEMENTS
Statements contained in this report that are not of historical fact are forward-looking statements intended to qualify for the safe harbors from liability established by the Private Securities Litigation Reform Act of 1995. These forward-looking statements can be identified as such because the statements include words such as “may,” “believe,” “expect,” “anticipate,” “plan,” “project,” “will,” “projections,” “estimate,” or other words of similar import. Similarly, statements that describe future financial performance or plans or strategies are forward-looking statements. Such forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from those expressed in, or implied by, such statements. Some, but not all, of the risks and uncertainties of Alliant Energy, IPL and WPL that could materially affect actual results include:

the direct or indirect effects resulting from the COVID-19 pandemic on sales volumes, margins, operations, employees, contractors, vendors, the ability to complete construction projects, supply chains, customers’ inability to pay bills, suspension of disconnects, the market value of the assets that fund pension plans and the potential for additional funding requirements, the ability of counterparties to meet their obligations, compliance with regulatory requirements, the ability to implement regulatory plans, economic conditions and access to capital markets;
the impact of penalties or third-party claims related to, or in connection with, a failure to maintain the security of personally identifiable information, including associated costs to notify affected persons and to mitigate their information security concerns;
the direct or indirect effects resulting from terrorist incidents, including physical attacks and cyber attacks, or responses to such incidents;
the impact of customer- and third party-owned generation, including alternative electric suppliers, in IPL’s and WPL’s service territories on system reliability, operating expenses and customers’ demand for electricity;
the impact of energy efficiency, franchise retention and customer disconnects on sales volumes and margins;
1

Table of Contents
the impact that price changes may have on IPL’s and WPL’s customers’ demand for electric, gas and steam services and their ability to pay their bills;
IPL’s and WPL’s ability to obtain adequate and timely rate relief to allow for, among other things, the recovery of and/or the return on costs, including fuel costs, operating costs, transmission costs, deferred expenditures, deferred tax assets, tax expense, capital expenditures, and remaining costs related to EGUs that may be permanently closed and certain other retired assets, decreases in sales volumes, earning their authorized rates of return, and the payments to their parent of expected levels of dividends;
federal and state regulatory or governmental actions, including the impact of legislation, and regulatory agency orders;
the ability to utilize tax credits and net operating losses generated to date, and those that may be generated in the future, before they expire;
the impacts of changes in tax rates, including adjustments made to deferred tax assets and liabilities;
employee workforce factors, including changes in key executives, ability to hire and retain employees with specialized skills, ability to create desired corporate culture, collective bargaining agreements and negotiations, work stoppages or restructurings;
any material post-closing payments related to any past asset divestitures, including the sale of Whiting Petroleum, which could result from, among other things, indemnification agreements, warranties, guarantees or litigation;
weather effects on results of utility operations;
issues associated with environmental remediation and environmental compliance, including compliance with all environmental and emissions permits, the CCR rule, future changes in environmental laws and regulations, including federal, state or local regulations for CO2 emissions reductions from new and existing fossil-fueled EGUs, and litigation associated with environmental requirements;
increased pressure from customers, investors and other stakeholders to more rapidly reduce CO2 emissions;
the ability to defend against environmental claims brought by state and federal agencies, such as the EPA, state natural resources agencies or third parties, such as the Sierra Club, and the impact on operating expenses of defending and resolving such claims;
continued access to the capital markets on competitive terms and rates, and the actions of credit rating agencies;
inflation and interest rates;
the ability to complete construction of solar projects within the cost caps set by regulators and the ability to efficiently utilize the solar project tax benefits for the benefit of customers;
changes in the price of delivered natural gas, transmission, purchased electricity and coal due to shifts in supply and demand caused by market conditions and regulations;
disruptions in the supply and delivery of natural gas, purchased electricity and coal;
the direct or indirect effects resulting from breakdown or failure of equipment in the operation of electric and gas distribution systems, such as mechanical problems and explosions or fires, and compliance with electric and gas transmission and distribution safety regulations, including regulations promulgated by the Pipeline and Hazardous Materials Safety Administration;
issues related to the availability and operations of EGUs, including start-up risks, breakdown or failure of equipment, performance below expected or contracted levels of output or efficiency, operator error, employee safety, transmission constraints, compliance with mandatory reliability standards and risks related to recovery of resulting incremental costs through rates;
impacts that excessive heat, excessive cold, storms or natural disasters may have on Alliant Energy’s, IPL’s and WPL’s operations and recovery of costs associated with restoration activities or on the operations of Alliant Energy’s investments;
Alliant Energy’s ability to sustain its dividend payout ratio goal;
changes to costs of providing benefits and related funding requirements of pension and OPEB plans due to the market value of the assets that fund the plans, economic conditions, financial market performance, interest rates, timing and form of benefits payments, life expectancies and demographics;
material changes in employee-related benefit and compensation costs;
risks associated with operation and ownership of non-utility holdings;
changes in technology that alter the channels through which customers buy or utilize Alliant Energy’s, IPL’s or WPL’s products and services;
impacts on equity income from unconsolidated investments from valuations and potential changes to ATC’s authorized return on equity;
impacts of IPL’s future tax benefits from Iowa rate-making practices, including deductions for repairs expenditures, allocation of mixed service costs and state depreciation, and recoverability of the associated regulatory assets from customers, when the differences reverse in future periods;
changes to the creditworthiness of counterparties with which Alliant Energy, IPL and WPL have contractual arrangements, including participants in the energy markets and fuel suppliers and transporters;
current or future litigation, regulatory investigations, proceedings or inquiries;
reputational damage from negative publicity, protests, fines, penalties and other negative consequences resulting in regulatory and/or legal actions;
the effect of accounting standards issued periodically by standard-setting bodies;
the ability to successfully complete tax audits and changes in tax accounting methods with no material impact on earnings and cash flows; and
other factors listed in MDA and Item 1A Risk Factors.

2

Table of Contents
Alliant Energy, IPL and WPL each assume no obligation, and disclaim any duty, to update the forward-looking statements in this report, except as required by law.

WEBSITE ACCESS TO REPORTS
Alliant Energy, IPL and WPL make their periodic and current reports, and amendments to those reports, available, free of charge, on Alliant Energy’s website at www.alliantenergy.com/investors on the same day as such material is electronically filed with, or furnished to, the SEC. Alliant Energy, IPL and WPL are not including the information contained on Alliant Energy’s website as a part of, or incorporating it by reference into, this report.

PART I

This report includes information relating to Alliant Energy, IPL and WPL (as well as AEF and Corporate Services). Where appropriate, information relating to a specific entity has been segregated and labeled as such. Unless otherwise noted, the information herein excludes discontinued operations for all periods presented. The terms “we,” “our” and “us” used in this report refer collectively to Alliant Energy, IPL and WPL.

ITEM 1. BUSINESS

A. GENERAL
Alliant Energy maintains its principal executive offices in Madison, Wisconsin. Alliant Energy operates as a regulated investor-owned public utility holding company, and its purpose-driven strategy is to serve its customers and build strong communities. Alliant Energy’s primary focus is to provide regulated electric and natural gas service to approximately 975,000 electric and approximately 420,000 natural gas customers in the Midwest through its two public utility subsidiaries, IPL and WPL. The primary first tier wholly-owned subsidiaries of Alliant Energy are as follows:

1) IPL - is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa. IPL provides utility services to incorporated communities as directed by the IUB and utilizes non-exclusive franchises, which cover the use of public right-of-ways for utility facilities in incorporated communities for a maximum term of 25 years. At December 31, 2020, IPL supplied electric and natural gas service to approximately 495,000 and 225,000 retail customers, respectively, in Iowa. IPL also sells electricity to wholesale customers in Minnesota, Illinois and Iowa. IPL is also engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa.

2) WPL - is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Wisconsin. WPL operates in municipalities pursuant to permits of indefinite duration and state statutes authorizing utility operation in areas annexed by a municipality. At December 31, 2020, WPL supplied electric and natural gas service to approximately 480,000 and 195,000 retail customers, respectively. WPL also sells electricity to wholesale customers in Wisconsin.

3) CORPORATE SERVICES - provides administrative services to Alliant Energy, IPL, WPL and AEF.

4) AEF - Alliant Energy’s non-utility holdings are organized under AEF, which manages a portfolio of wholly-owned subsidiaries and additional holdings, including the following distinct platforms:

ATI - currently holds all of Alliant Energy’s interest in ATC Holdings. ATC Holdings is comprised of a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC. ATC is an independent, for-profit, transmission-only company. ATC Holdco LLC holds Duke-American Transmission Company, LLC, a joint venture between Duke Energy Corporation and ATC, that owns electric transmission infrastructure in North America.

Non-utility Wind Farm - includes a 50% cash equity ownership interest in a 225 MW non-utility wind farm located in Oklahoma.

Sheboygan Falls Energy Facility - is a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is leased to WPL for an initial period of 20 years ending in 2025.

Travero - formerly known as Transportation, Travero owns and operates a short-line rail freight service in Iowa; a barge, rail and truck freight terminal on the Mississippi River; freight brokerage and logistics management services; and a rail-served warehouse in Alliant Energy’s Big Cedar Industrial Center Mega-site in Cedar Rapids, Iowa, which is currently scheduled to open later in 2021.


3

Table of Contents
B. INFORMATION RELATING TO ALLIANT ENERGY ON A CONSOLIDATED BASIS

1) HUMAN CAPITAL MANAGEMENT - Our purpose to serve customers and build strong communities, as well as our values, are the foundation of our culture, guide our actions, and describe how we accomplish our strategy. We work to attract, retain, reward and develop a diverse and qualified workforce of high-performing employees and teams because our employees and culture are critical to our strategy.

Employees - At December 31, 2020, Alliant Energy, IPL and WPL had the following full- and part-time employees:
TotalNumber ofPercentage of Employees
Number ofBargaining UnitCovered by Collective
EmployeesEmployeesBargaining Agreements
Alliant Energy3,3751,792 53%
IPL1,176804 68%
WPL1,072879 82%

The majority of IPL’s bargaining unit employees are covered by the International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) collective bargaining agreement, which expires on August 31, 2024. All of WPL’s bargaining unit employees are covered by the International Brotherhood of Electrical Workers Local 965 collective bargaining agreement, which expires on May 31, 2022.

Safety - Safety is integral to our company’s culture. It is one of our Values – “Live safety. Everyone. Always. Our first priority is that nobody gets hurt.” Alliant Energy is committed to providing a safe environment for our employees, visitors, customers, contractors, vendors and the communities in which we live and work.

We focus on the proactive management of our safety performance. Our comprehensive program includes leading indicators such as tracking and reporting near misses and unsafe conditions, which we believe helps prevent similar incidents from occurring elsewhere. We also conduct internal safety assessments of our generating facilities.

We maintain executive and local safety leadership teams to establish our safety vision, strategy and priorities, as well as ensure education and recognition of employee actions that improve our safety culture. This leadership provides strong support for sustained growth of both employee and public safety programs and initiatives.

Public safety is equally important as we interact with our customers to provide energy to their homes and businesses. We offer awareness campaigns, natural gas and electric public safety presentations, and free online resources and training programs and guidance to assist local emergency responders.

Total Rewards - Our market-competitive Total Rewards programs are designed to meet the varied and evolving needs of our employees and their families. Through a variety of flexible health and wellness programs, we offer employees choice, support their financial, physical, and mental well-being, provide tools and resources to help improve or maintain their health status, and promote engagement in healthy behaviors.

In addition to competitive salaries and wages, our Total Rewards programs include:
a 401(k) savings plan with an employer match;
healthcare and insurance benefits, including medical, vision, dental, life, short-term disability, and long-term disability insurance;
health savings and flexible spending accounts;
paid time off to use for vacation, personal time, sick time, holidays, bereavement, jury duty, military leave, parental leave, maternity leave, and adoption leave;
family care resources;
adoption assistance;
legal planning assistance;
Employee Assistance Program;
tuition reimbursement;
Vacation Donation Program; and
Volunteer Grants & Matching Gifts Program.

Diversity, Equity and Inclusion (DE&I) - A diverse, equitable and inclusive workplace is crucial for the success and retention of our employees, to attract future talent and to execute our purpose-driven strategy to serve our customers and build strong communities. It is one of our Values – “Care for others: Together we create a workplace where people feel like they belong and can use their unique backgrounds, talents and perspectives to their fullest potential.”

Our efforts to create a diverse and inclusive workforce include:
learning opportunities for employees, such as inviting employees to participate in area diversity summits and supporting company-wide listening sessions, speakers and programs;
4

Table of Contents
Employee Resource Groups that foster a diverse and inclusive workplace that supports employee well-being while promoting professional development and enhancing community relationships; and
a DE&I Leadership Team that partners with the Human Resources recruiting department and hiring managers to attract more diverse applicants.

Our DE&I initiatives also include a focus on building a diverse Board of Directors. We believe it is in our shareowners’ best interest to have a diverse Board representing a wide breadth of experiences and perspectives. Our Board currently has approximately 33% gender diversity and 22% ethnic diversity.

Our 2020 DE&I accomplishments include:
received a perfect score on the Corporate Equality Index administered by the Human Rights Campaign Foundation to benchmark LGBTQ+ rights, policies and practices;
held a Day of Understanding where executives met with employees and held conversations about unconscious bias; and
selected for the 2020 Bloomberg Gender-Equality Index.

Alliant Energy’s short-term incentive compensation plan includes diversity metrics to drive leadership accountability for efforts to advance a diverse and inclusive culture.

Talent Development and Workforce Readiness - We support employees in the growth of their careers through several training opportunities and development programs. These include tuition reimbursement, online, instructor-led and on-the-job learning formats, as well as leadership development and succession planning.

In addition, we have an apprenticeship program that combines supervised, structured on-the-job training with related instruction to produce highly skilled trade and technical workers. Our program builds lifetime skills and comprehensive knowledge in the high-demand technical trades necessary for our success. The program gives us the flexibility to tailor training to match our needs – training employees in our facilities, on our equipment, and consistent with our safety standards and employee expectations. We instill company Values, methods and procedures from day one.

2) REGULATION - Alliant Energy, IPL and WPL are subject to regulation by various federal, state and local agencies. The following includes the primary regulations impacting Alliant Energy’s, IPL’s and WPL’s businesses.

FERC -
Public Utility Holding Company Act of 2005 - Alliant Energy is registered with FERC as a public utility holding company, pursuant to the Public Utility Holding Company Act of 2005, and is required to maintain certain records and to report certain transactions involving its public utilities, service company and other entities regulated by FERC. Corporate Services, IPL and WPL are subject to regulation by FERC under the Public Utility Holding Company Act of 2005 for various matters including, but not limited to, affiliate transactions, public utility mergers, acquisitions and dispositions, and books, records and accounting requirements.

Energy Policy Act - The Energy Policy Act requires creation of an Electric Reliability Organization to provide oversight by FERC. FERC designated North American Electric Reliability Corporation as the overarching Electric Reliability Organization. Midwest Reliability Organization, which is a regional member of North American Electric Reliability Corporation, has direct responsibility for mandatory electric reliability standards for IPL and WPL.

Federal Power Act - FERC also has jurisdiction, under the Federal Power Act, over certain electric utility facilities and operations, electric wholesale and transmission rates, dividend payments, issuance of IPL’s securities, and accounting practices of Corporate Services, IPL and WPL.

Electric Wholesale Rates - IPL and WPL receive wholesale electric market-based rate authority from FERC. Market-based rate authorization allows for wholesale sales of electricity within the MISO market and in transactions directly with third parties, based on the market value of the transactions. IPL and WPL also have FERC-approved cost of service formula-based rates related to the provision of firm full- and partial-requirement wholesale electric sales, which allow for true-ups to actual costs, including fuel costs.

Electric Transmission Rates - FERC regulates the rates charged for electric transmission facilities used in interstate commerce. IPL and WPL do not own or operate electric transmission facilities; however, both IPL and WPL pay for the use of the interstate electric transmission system based upon FERC-regulated rates. IPL and WPL rely primarily on the use of the ITC and ATC transmission systems, respectively.

Natural Gas Act - FERC regulates the transportation and sale for resale of natural gas in interstate commerce under the Natural Gas Act. Under the Natural Gas Act, FERC has authority over certain natural gas facilities and operations of IPL and WPL.

5

Table of Contents
IUB - IPL is subject to regulation by the IUB for various matters including, but not limited to, retail utility rates and standards of service, accounting requirements, sales of assets with values that exceed 3% of IPL’s revenues, and approval of the location and construction of EGUs.

Retail Utility Base Rates - IPL files periodic requests with the IUB for retail rate changes and may base those requests on either historical or forward-looking test periods. The IUB must decide on requests for retail rate changes within 10 months of the date of the application for which changes are filed. The historical test periods may be adjusted for certain known and measurable changes to capital investments, cost of capital and operating and maintenance expenses consistent with IUB rules and regulations. Forward-looking test periods must follow established regulatory principles as applied to the forecasted information and include a requirement for a subsequent proceeding review after the close of the forward-looking test period to evaluate whether actual costs and revenue were reasonably consistent with the forward-looking test period.

Energy Efficiency - In accordance with Iowa law, IPL is required to file an EEP every five years with the IUB. An EEP provides a utility’s plan and related budget to achieve specified levels of electric and gas energy savings. IUB approval demonstrates that IPL’s EEP is reasonably expected to achieve cost-effective delivery of the energy efficiency programs. Refer to Note 1(g) for discussion of the recovery of these costs from IPL’s retail electric and gas customers.

Electric Generating Units - IPL must obtain a certificate of public convenience, use and necessity (GCU Certificate) from the IUB in order to construct a new, or significantly alter (including fuel switching) an existing, EGU located in Iowa with 25 MW or more of capacity. IPL’s ownership and operation of EGUs (including those located outside the state of Iowa) to serve Iowa customers is subject to retail utility rate regulation by the IUB.

Gas Pipeline Projects - IPL must obtain a pipeline permit from the IUB related to the siting of utility gas pipelines in Iowa that will be operated at a pressure over 150 pounds per square inch and will transport gas to a distribution system or single, large volume customer.

Advance Rate-making Principles - Iowa law provides Iowa utilities with rate-making principles prior to making certain generation investments in Iowa. As a result, IPL may file for, and the IUB must render a decision on, rate-making principles for certain new EGUs located in Iowa, including any alternative energy production facility (such as a wind or solar facility), combined-cycle natural gas-fired EGU, and certain base-load EGUs with a nameplate generating capacity of 300 MW or more (such as nuclear or coal-fired generation). Advance rate-making principles are also available for the repowering of an alternative energy production facility or certain significant alterations of an existing EGU. Upon approval of rate-making principles by the IUB, IPL must either build the EGU or repower the alternative energy production facility under the approved rate-making principles, or not at all.

Electric Generating Unit Environmental Controls Projects - IPL is required to submit an updated emissions plan and budget biennially to the IUB setting out a multi-year plan and budget for managing regulated emissions from its coal-fired EGUs in a cost-effective manner. IPL must simultaneously submit this plan and budget to the Iowa Department of Natural Resources for a determination of whether the plan and budget meet state environmental requirements for regulated emissions. The reasonable and prudent costs associated with implementing the approved plan are expected to be included in IPL’s future retail electric rates.

PSCW - WPL is subject to regulation by the PSCW related to its operations in Wisconsin for various matters including, but not limited to, retail utility rates and standards of service, accounting requirements, issuance and use of proceeds of securities, affiliate transactions, approval of the location and construction of EGUs and certain other additions and extensions to facilities. In addition, Alliant Energy is subject to regulation by the PSCW for the type and amount of Alliant Energy’s holdings in non-utility businesses and other affiliated interest activities, among other matters.

Retail Utility Base Rates - WPL files periodic requests with the PSCW for retail rate changes. These filings are required to be based on forward-looking test periods. There is no statutory time limit for the PSCW to decide on retail base rate requests. However, the PSCW attempts to process retail base rate reviews in approximately 10 months and has the ability to approve interim retail rate relief, subject to refund, if necessary. Currently, WPL is required to defer a portion of its earnings if its annual regulatory return on common equity exceeds certain levels.

Public Benefits - WPL contributes 1.2% of its annual retail utility revenues to help fund Focus on Energy, Wisconsin’s state-wide energy efficiency and renewable energy resource program. In addition, WPL contributes to a program that provides assistance to income-eligible residents in Wisconsin. These contributions are recovered from customers through a bill surcharge of up to 3% of customers’ utilities bills. Refer to Note 1(g) for discussion of the recovery of these costs from WPL’s retail electric and gas customers.

New Electric Generating Units - A CA application is required to be filed with the PSCW for construction approval of any new EGU with a capacity of less than 100 MW and a project cost of $11.0 million or more. WPL must obtain a CPCN from the PSCW in order to construct a new EGU in Wisconsin with a capacity of 100 MW or more. In addition, WPL’s ownership and operation of EGUs (including those located outside the state of Wisconsin) to serve Wisconsin customers are subject to retail utility rate regulation by the PSCW.
6

Table of Contents

Electric Generating Unit Upgrades and Electric Distribution Projects - A CA application is required to be filed with the PSCW for construction approval of any additions to EGUs, including environmental controls projects, as well as electric distribution projects, with estimated project costs of $11.0 million or more.

Gas Distribution Projects - A CA application is required to be filed with the PSCW for construction approval of gas projects with an estimated project cost of $2.5 million or more and at any time that WPL requests to extend gas service to a new portion of its service territory.

Advance Rate-making Principles - Wisconsin law provides Wisconsin utilities with the opportunity to request rate-making principles prior to the purchase or construction of any EGU utilized to serve Wisconsin customers. WPL is not obligated to file for or accept authorized rate-making principles under Wisconsin law. WPL can proceed with an approved project under traditional rate-making terms or accept authorized rate-making principles under Wisconsin law.

Environmental - Alliant Energy, IPL and WPL are subject to regulation of environmental matters by federal, state and local authorities as a result of their current and past operations. Alliant Energy, IPL and WPL monitor these environmental matters and address them by installing controls that reduce emissions and by implementing operational modifications or other measures to address compliance obligations. There is currently significant regulatory uncertainty with respect to environmental rules and regulations discussed below. Given the dynamic nature of environmental regulations and other related regulatory requirements, Alliant Energy, IPL and WPL have compliance plans to address these environmental obligations. Prudent expenditures incurred by IPL and WPL to comply with environmental requirements are eligible to be recovered in rates from their customers. The following are major environmental matters that could potentially have a significant impact on financial condition and results of operations.

Climate Change and Greenhouse Gases Regulations - There is continued deliberation on the public policy that the U.S. should adopt to address climate change, including assessment of both domestic actions and international efforts. In 2007, the Supreme Court provided direction on the EPA’s authority to regulate GHG and ruled that these emissions are covered by the CAA. In 2009, the EPA issued a ruling that found GHG emissions contribute to climate change, and therefore, threaten public health and welfare, which was the prerequisite for implementing carbon reduction standards under the CAA. While the EPA’s rules to regulate GHG issued under the authority of the CAA remain subject to further review, growing emphasis on climate change and evolving energy technologies are driving efforts to decarbonize the environment through voluntary emissions reductions. The primary GHG directly emitted from Alliant Energy’s utility operations is CO2 from the combustion of fossil fuels at their larger EGUs.

Clean Air Act Section 111(d) - In 2015, the EPA published final standards under Section 111(d) of the CAA, referred to as the Clean Power Plan, to reduce CO2 emissions from existing fossil-fueled EGUs. In July 2019, the EPA published the final Affordable Clean Energy rule, which repealed the Clean Power Plan effective September 6, 2019. The Affordable Clean Energy rule established emission guidelines for states to develop plans by July 2022 to reduce CO2 emissions from existing coal-fired EGUs. In January 2021, the U.S. Court of Appeals for the District of Columbia Circuit vacated the Affordable Clean Energy rule and remanded the rule back to the EPA for reconsideration. Alliant Energy, IPL and WPL are currently unable to predict with certainty the future outcome or impact of these matters.

Clean Air Act Section 111(b) - In 2015, the EPA published final standards under Section 111(b) of the CAA, which establish CO2 emissions limits for certain new fossil-fueled EGUs. Marshalltown and West Riverside are subject to the EPA’s Section 111(b) regulation and have been designed to achieve compliance with these standards. Litigation related to Section 111(b) is suspended while the EPA revises Section 111(b), and Alliant Energy, IPL and WPL are currently unable to predict with certainty the impact of these standards. In January 2021, the EPA published a final rule establishing that EGUs are a significant source of GHG and reaffirming that CO2 emissions from EGUs can be regulated under Section 111 of the CAA.

Water Quality -
Effluent Limitation Guidelines - In 2015, the EPA published final effluent limitation guidelines, which required changes to discharge limits for wastewater from certain IPL and WPL steam EGUs. In December 2020, revised effluent limitation guidelines became effective, which incorporated flexibility to the 2015 rule, including a new subcategory for coal-fired EGUs that will be retired or converted to no longer burn coal before 2028. Compliance for existing steam-electric generating facilities is determined by each facility’s wastewater discharge permit and will generally be required by December 31, 2025. Projects required for compliance are facility-specific. Estimated capital expenditures to comply with the December 2020 guidelines for 2021 through 2024 are included in the “Other Generation” line in the construction and acquisition expenditures table in “Liquidity and Capital Resources” in MDA. In January 2021, the new Presidential Administration issued an Executive Order requiring the review and possible revision of environmental regulations issued during the prior Administration. Alliant Energy, IPL and WPL are currently unable to predict with certainty the future outcome or impact of the January 2021 Executive Order.

Land and Solid Waste -
Coal Combustion Residuals Rule - The final CCR Rule, which regulates CCR as a non-hazardous waste, became effective in 2015. IPL and WPL have coal-fired EGUs with coal ash ponds and active CCR landfills that are impacted by this rule.
7

Table of Contents
Litigation related to the CCR Rule remains on-going and has resulted in various proposed rule updates. Alliant Energy, IPL and WPL are currently unable to predict with certainty the impact of these updates.

MGP Sites - Refer to Note 17(e) for discussion of IPL’s and WPL’s MGP sites.

Renewable Energy Standards - Iowa and Wisconsin have renewable energy standards, which establish the minimum amount of energy IPL and WPL must supply from renewable resources. IPL primarily relies upon renewable energy generated from the wind resources it owns and renewable energy acquired under PPAs to meet these requirements. WPL utilizes its current renewable portfolio, which primarily consists of wind and hydro energy, both owned and acquired under PPAs, to meet these requirements. IPL and WPL currently exceed their respective renewable energy standards requirements.

3) STRATEGY - Refer to “Overview” in MDA for discussion of Alliant Energy’s strategy, which supports its mission to deliver energy solutions and exceptional service that its customers and communities count on - safely, efficiently and responsibly.

C. INFORMATION RELATING TO UTILITY OPERATIONS
Alliant Energy’s utility business (IPL and WPL) has three segments: a) electric operations; b) gas operations; and c) other, which includes IPL’s steam operations and the unallocated portions of the utility business. IPL’s and WPL’s electric, gas and other revenues as a percentage of total revenues were as follows:
IPLWPL
lnt-20201231_g2.jpglnt-20201231_g3.jpglnt-20201231_g4.jpglnt-20201231_g5.jpg
1) ELECTRIC UTILITY OPERATIONS
General - Electric utility operations represent the largest operating segment for Alliant Energy, IPL and WPL. Alliant Energy’s electric utility operations are located in the Midwest with IPL providing retail electric service in Iowa and WPL providing retail and wholesale electric service in Wisconsin. IPL also sells electricity to wholesale customers in Minnesota, Illinois and Iowa. Refer to the “Electric Operating Information” tables for additional details regarding electric utility operations.

Customers - IPL and WPL provide electric utility service to a diversified base of retail customers in several industries, with the largest concentrations in the farming, agriculture, industrial manufacturing, chemical (including ethanol), packaging and food industries. IPL and WPL also sell electricity to wholesale customers, which primarily consist of municipalities and rural electric cooperatives.

Seasonality - Electric sales are seasonal to some extent with the annual peak normally occurring in the summer months due to air conditioning requirements. Electric sales are also impacted to a certain extent in the winter months due to heating requirements.

Competition - Retail electric customers in Iowa and Wisconsin currently do not have the ability to choose their electric supplier, and IPL and WPL have obligations to serve all their retail electric customers. Although electric service in Iowa and Wisconsin is regulated, IPL and WPL still face competition from self-generation by large industrial customers, customer- and third party-owned generation (e.g. solar panels), alternative energy sources, and petitions to municipalize (Iowa) as well as service territory expansions by municipal utilities through annexations (Wisconsin). In addition, the wholesale power market is competitive and IPL and WPL compete against independent power producers, other utilities and MISO market purchases to serve wholesale customers for their electric energy and capacity needs. Alliant Energy’s strategy includes actions to retain current customers and attract new customers into IPL’s and WPL’s service territories in an effort to keep energy rates low for all of their customers. Refer to “Overview” in MDA for discussion of the strategy element focusing on growing customer demand.

Electric Supply - Alliant Energy, IPL and WPL have met, and expect to continue meeting, customer demand of electricity through a mix of electric supply, including owned EGUs, PPAs and additional purchases from wholesale energy markets. Alliant Energy expects its mix of electric supply to change in the next several years with IPL’s and WPL’s planned solar generation and the proposed retirement and/or fuel switching of various EGUs, as well as the potential sale of partial interests in West Riverside to neighboring utilities. Long-term generation plans are intended to meet customer demand, reduce air emissions and water impacts, reduce reliance on wholesale market purchases and mitigate the impacts of future EGU
8

Table of Contents
retirements while maintaining compliance with long-term electric demand planning reserve margins, renewable energy standards established by regulators and other various requirements.

Electric Demand Planning Reserve Margin - IPL and WPL are required to maintain a planning reserve margin above their load at the time of the MISO-wide peak to ensure reliability of electric service to their customers. The required installed capacity reserve margin is 18.3% and the required unforced capacity reserve margin is 9.4% for the June 1, 2021 through May 31, 2022 MISO planning year. IPL and WPL currently have adequate capacity to meet such MISO planning reserve margin requirements.

Generation Fuel Supply - IPL and WPL own a portfolio of EGUs located in Iowa, Wisconsin and Minnesota with a diversified fuel mix that includes natural gas, renewable resources and coal. Refer to “Properties” in Item 2 for details of IPL’s and WPL’s EGUs. The average cost of delivered fuel per million British Thermal Units used for electric generation was as follows:
IPLWPL
202020192018202020192018
All fuels$2.22 $2.17 $2.46 $2.36 $2.55 $2.72 
Natural gas (a)2.54 2.52 3.12 2.51 2.76 3.30 
Coal1.84 1.81 1.97 2.19 2.35 2.45 

(a)The average cost of natural gas includes commodity and transportation costs, as well as realized gains and losses from swap and option contracts used to hedge the price of natural gas volumes expected to be used by IPL’s and WPL’s natural gas-fired EGUs.

Natural Gas - Alliant Energy, IPL and WPL own several natural gas-fired EGUs, and WPL also has exclusive rights to the output of AEF’s Sheboygan Falls Energy Facility under an affiliated lease agreement. These facilities help meet customer demand for electricity when natural gas prices are low enough to make natural gas-fired generation economical compared to other fuel sources. Alliant Energy manages the gas supply to these gas-fired EGUs and helps ensure an adequate supply is available at known prices through a combination of gas commodity, pipeline transportation and storage agreements held by IPL and WPL for numerous years. Alliant Energy, IPL and WPL believe they are reasonably insulated against gas price volatility for these EGUs given their use of forward contracts and hedging practices, as well as their regulatory cost-recovery mechanisms.

Coal - Coal is one of the fuel sources for owned EGUs. Coal contracts entered into with different entities help ensure that a specified supply of coal is available, and delivered, at known prices for IPL’s and WPL’s coal-fired EGUs. Alliant Energy, IPL and WPL believe their coal supply portfolio represents a reasonable balance between the risks of insufficient supplies and those associated with being unable to respond to future coal market changes. Remaining coal requirements are expected to be met from either future term contracts or purchases in the spot market. Currently, all of the coal utilized by IPL and WPL is from the Wyoming Powder River Basin.

Alliant Energy, IPL and WPL believe they are reasonably insulated against coal price volatility given their current coal procurement process, the specific coal market in their primary purchase region and regulatory cost-recovery mechanisms. The coal procurement process supports periodic purchases, staggering of contract terms, stair-stepped levels of supply going forward and supplier diversity. Similarly, given the term lengths of their transportation agreements and strategic alignment of agreement expirations for negotiation purposes, Alliant Energy, IPL and WPL believe they are reasonably insulated against future higher coal transportation rates from the major railroads.

Purchased Power - IPL and WPL periodically enter into PPAs and purchase electricity from wholesale energy markets to meet a portion of their customer demand for electricity.

Electric Transmission - IPL and WPL do not own electric transmission service assets and currently receive transmission services from ITC and ATC, respectively. ITC and ATC are independent, for-profit, transmission-only companies and are transmission-owning members of the MISO Regional Transmission Organization, Midwest Reliability Organization and Reliability First Corporation Regional Entities. The annual transmission service rates that ITC or ATC charges their customers are calculated each calendar year using a FERC-approved cost of service formula rate. As a result, ITC and ATC can implement new rates each calendar year without filing a request with FERC. However, new rates are subject to challenge by either FERC or customers. If the rates proposed by ITC or ATC are determined by FERC to be unjust or unreasonable, or another mechanism is determined by FERC to be just and reasonable, ITC’s or ATC’s rates would change accordingly. Refer to Note 1(g) for discussion of a transmission cost rider utilized by IPL for recovery of its electric transmission service expense, and discussion of WPL’s electric transmission service expense, which is recovered from its retail electric customers through changes in base rates determined during periodic rate proceedings. Refer to Note 17(g) for discussion of MISO transmission owner return on equity complaints.

9

Table of Contents
MISO Markets - IPL and WPL are members of MISO, a FERC-approved Regional Transmission Organization, which is responsible for monitoring and ensuring equal access to the transmission system in their footprint. IPL and WPL participate in the wholesale energy and ancillary services markets operated by MISO, which are discussed in more detail below. As agent for IPL and WPL, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases between IPL and WPL based on statements received from MISO.

Wholesale Energy Market - IPL and WPL sell and purchase power in the day-ahead and real-time wholesale energy markets operated by MISO. MISO’s bid/offer-based markets compare the cost of IPL and WPL generation against other generators, which affects IPL and WPL generation operations, energy purchases and energy sales. MISO generally dispatches the lowest cost generators, while recognizing current system constraints, to reduce costs for purchasers in the wholesale energy market. In addition, MISO may dispatch generators that support reliability needs, but that would not have operated based on economic needs. In these cases, MISO’s settlement assures that these generators are made whole financially for their variable costs.

Ancillary Services Market - IPL and WPL also participate in MISO’s ancillary services market, which integrates the procurement and use of regulation and contingency reserves with the existing wholesale energy market to ensure reliability of electricity supply. MISO’s ancillary services market has had the overall impact of lowering ancillary services costs in the MISO footprint.

Financial Transmission Rights and Auction Revenue Rights - In areas of constrained transmission capacity, energy costs could be higher due to congestion and its impact on locational marginal prices. FTRs provide a hedge for certain congestion costs that occur in the MISO energy market. MISO allocates auction revenue rights to IPL and WPL annually based on a fiscal year from June 1 through May 31 and historical use of the transmission system. The allocated auction revenue rights are used by IPL and WPL to acquire FTRs through the FTR auctions operated by MISO.

Resource Adequacy - MISO has resource adequacy requirements to help ensure adequate resources to meet forecasted peak load obligations plus a reserve margin. Only accredited capacity assigned to EGUs is available to meet these requirements. In order for an EGU to receive accredited capacity, it must meet MISO capacity accreditation requirements, which can include satisfying transmission requirements identified in its interconnection agreement prior to the MISO planning year.

10

Table of Contents
Electric Operating Information - Alliant Energy202020192018
Revenues (in millions):
Residential$1,093 $1,092 $1,063 
Commercial718 770 736 
Industrial841 889 889 
Retail subtotal2,652 2,751 2,688 
Sales for resale204 250 259 
Other64 63 53 
Total$2,920 $3,064 $3,000 
Sales (000s MWh):
Residential7,294 7,207 7,367 
Commercial6,107 6,466 6,487 
Industrial11,134 11,448 11,830