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v2.4.1.9

Summary Of Significant Accounting Policies (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2014 customer
IPL [Member] |
General: |
Generation and distribution of steam, number of customers served (in customers) | 2 lnt_GenerationAndDistributionOfSteamNumberOfCustomersServed / dei_LegalEntityAxis = lnt_IplMember
Property, Plant and Equipment: |
Accrual recorded, percentage of estimated CWIP | 100.00%lnt_PublicUtilitiesAllowanceForFundsUsedDuringConstructionReturnEarnedExpectedPercentageOfEstimatedConstructionWorkInProcessNextTwelveMonths / dei_LegalEntityAxis = lnt_IplMember
Operating Revenues: |
Estimated recovery of overaccrued operating revenue, reflected on customer billing, maximum period | 2 years
WPL [Member] |
Property, Plant and Equipment: |
Accrual recorded, percentage of estimated CWIP | 50.00%lnt_PublicUtilitiesAllowanceForFundsUsedDuringConstructionReturnEarnedExpectedPercentageOfEstimatedConstructionWorkInProcessNextTwelveMonths / dei_LegalEntityAxis = lnt_WplMember
Recovery rates, projects with approval | 100.00%lnt_RecoveryRatesForProjectsWithApproval / dei_LegalEntityAxis = lnt_WplMember
Operating Revenues: |
Final settlement recovery of overaccrued operating revenue, reflected on customer billing, maximum period | 2 years
Sheboygan Falls Energy Facility [Member] |
General: |
Fossil-fueled EGU capacity (in megawatts) | 347 lnt_FossilFueledEnergyGeneratingUnitsCapacity / us-gaap_PublicUtilityAxis = lnt_SheboyganFallsEnergyFacilityMember
Capital lease, lease term | 20 years
Franklin County Wind Project [Member] |
General: |
Wind EGU capacity (in megawatts) | 99 lnt_ElectricCapacityOfWindProject / us-gaap_PublicUtilityAxis = lnt_FranklinCountyWindProjectMember

X
- Definition Capital Leases, Lease Term + References No definition available. + Details
Name: | lnt_CapitalLeasesLeaseTerm
Namespace Prefix: | lnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Electric Capacity Of Wind Project + References No definition available. + Details
Name: | lnt_ElectricCapacityOfWindProject
Namespace Prefix: | lnt_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Estimated Recovery of Overaccrued Operating Revenue, Reflected on Customer Billing, Maximum Period + References No definition available. + Details
Name: | lnt_EstimatedRecoveryOfOveraccruedOperatingRevenueReflectedOnCustomerBillingMaximumPeriod
Namespace Prefix: | lnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Final Settlement Recovery of Overaccrued Operating Revenue, Reflected on Customer Billing, Maximum Period + References No definition available. + Details
Name: | lnt_FinalSettlementRecoveryOfOveraccruedOperatingRevenueReflectedOnCustomerBillingMaximumPeriod
Namespace Prefix: | lnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fossil Fueled Energy Generating Units Capacity + References No definition available. + Details
Name: | lnt_FossilFueledEnergyGeneratingUnitsCapacity
Namespace Prefix: | lnt_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | lnt_GeneralAbstract
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Generation and Distribution of Steam, Number of Customers Served + References No definition available. + Details
Name: | lnt_GenerationAndDistributionOfSteamNumberOfCustomersServed
Namespace Prefix: | lnt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Public Utilities, Allowance for Funds Used During Construction, Return Earned, Expected Percentage of Estimated Construction Work-in-process, Next Twelve Months + References No definition available. + Details
Name: | lnt_PublicUtilitiesAllowanceForFundsUsedDuringConstructionReturnEarnedExpectedPercentageOfEstimatedConstructionWorkInProcessNextTwelveMonths
Namespace Prefix: | lnt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Recovery Rates For Projects With Approval + References No definition available. + Details
Name: | lnt_RecoveryRatesForProjectsWithApproval
Namespace Prefix: | lnt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RevenuesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=lnt_FranklinCountyWindProjectMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PublicUtilityAxis=lnt_SheboyganFallsEnergyFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |