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Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2007 | Dec. 31, 2011
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | $ 2,360 us-gaap_LongTermPurchaseCommitmentAmount |  |  |
Individual commitments incurred | 1 lnt_IndividualCommitmentsIncurred |  |  |
Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1,746 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember | [1] |  |
DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1,538 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember | [1],[2] |  |
Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 208 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember | [1] |  |
Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 278 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember |  |  |
Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 291 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember | [3] |  |
SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 34 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember | [4] |  |
Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 11 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember | [5] |  |
2015 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 514 us-gaap_LongTermPurchaseCommitmentAmount / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember |  |  |
2015 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 193 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [1] |  |
2015 [Member] | DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 119 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [1],[2] |  |
2015 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 74 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [1] |  |
2015 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 175 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember |  |  |
2015 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 124 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [3] |  |
2015 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 12 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [4] |  |
2015 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 10 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [5] |  |
2016 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 333 us-gaap_LongTermPurchaseCommitmentAmount / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember |  |  |
2016 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 171 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [1] |  |
2016 [Member] | DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 125 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [1],[2] |  |
2016 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 46 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [1] |  |
2016 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 69 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember |  |  |
2016 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 78 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [3] |  |
2016 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 14 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [4] |  |
2016 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [5] |  |
2017 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 260 us-gaap_LongTermPurchaseCommitmentAmount / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember |  |  |
2017 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 182 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [1] |  |
2017 [Member] | DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 138 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [1],[2] |  |
2017 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 44 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [1] |  |
2017 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 23 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember |  |  |
2017 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 47 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [3] |  |
2017 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 8 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [4] |  |
2017 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [5] |  |
2018 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 214 us-gaap_LongTermPurchaseCommitmentAmount / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember |  |  |
2018 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 175 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [1] |  |
2018 [Member] | DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 131 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [1],[2] |  |
2018 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 44 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [1] |  |
2018 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 5 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember |  |  |
2018 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 34 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [3] |  |
2018 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [4] |  |
2018 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [5] |  |
2019 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 153 us-gaap_LongTermPurchaseCommitmentAmount / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember |  |  |
2019 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 143 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [1] |  |
2019 [Member] | DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 143 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [1],[2] |  |
2019 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [1] |  |
2019 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 2 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember |  |  |
2019 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 8 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [3] |  |
2019 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [4] |  |
2019 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [5] |  |
Thereafter [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 886 us-gaap_LongTermPurchaseCommitmentAmount / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember |  |  |
Thereafter [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 882 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [1] |  |
Thereafter [Member] | DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 882 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [1],[2] |  |
Thereafter [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [1] |  |
Thereafter [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 4 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember |  |  |
Thereafter [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [3] |  |
Thereafter [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [4] |  |
Thereafter [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [5] |  |
IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1,859 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember |  |  |
IPL [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1,539 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember | [1] |  |
IPL [Member] | DAEC IPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Approved amount of electric power capacity (in megawatts) | 431 lnt_LongTermPurchaseCommitmentApprovedAmountOfElectricPowerCapacity / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember |  |  |
IPL [Member] | DAEC [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1,538 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecMember | [1],[2] |  |
IPL [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember | [1] |  |
IPL [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 153 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember |  |  |
IPL [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 127 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember | [3] |  |
IPL [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 34 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember | [4] | 34 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember |
IPL [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 6 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember | [5] |  |
IPL [Member] | 2015 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 306 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember |  |  |
IPL [Member] | 2015 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 119 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [1] |  |
IPL [Member] | 2015 [Member] | DAEC [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 119 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [1],[2] |  |
IPL [Member] | 2015 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [1] |  |
IPL [Member] | 2015 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 108 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember |  |  |
IPL [Member] | 2015 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 61 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [3] |  |
IPL [Member] | 2015 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 12 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [4] |  |
IPL [Member] | 2015 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 6 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [5] |  |
IPL [Member] | 2016 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 207 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember |  |  |
IPL [Member] | 2016 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 126 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [1] |  |
IPL [Member] | 2016 [Member] | DAEC [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 125 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [1],[2] |  |
IPL [Member] | 2016 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [1] |  |
IPL [Member] | 2016 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 32 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember |  |  |
IPL [Member] | 2016 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 35 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [3] |  |
IPL [Member] | 2016 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 14 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [4] |  |
IPL [Member] | 2016 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [5] |  |
IPL [Member] | 2017 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 171 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember |  |  |
IPL [Member] | 2017 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 138 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [1] |  |
IPL [Member] | 2017 [Member] | DAEC [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 138 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [1],[2] |  |
IPL [Member] | 2017 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [1] |  |
IPL [Member] | 2017 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 5 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember |  |  |
IPL [Member] | 2017 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 20 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [3] |  |
IPL [Member] | 2017 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 8 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [4] |  |
IPL [Member] | 2017 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [5] |  |
IPL [Member] | 2018 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 144 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember |  |  |
IPL [Member] | 2018 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 131 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [1] |  |
IPL [Member] | 2018 [Member] | DAEC [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 131 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [1],[2] |  |
IPL [Member] | 2018 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [1] |  |
IPL [Member] | 2018 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 2 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember |  |  |
IPL [Member] | 2018 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 11 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [3] |  |
IPL [Member] | 2018 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [4] |  |
IPL [Member] | 2018 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [5] |  |
IPL [Member] | 2019 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 145 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember |  |  |
IPL [Member] | 2019 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 143 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [1] |  |
IPL [Member] | 2019 [Member] | DAEC [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 143 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [1],[2] |  |
IPL [Member] | 2019 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [1] |  |
IPL [Member] | 2019 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 2 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember |  |  |
IPL [Member] | 2019 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [3] |  |
IPL [Member] | 2019 [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [4] |  |
IPL [Member] | 2019 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [5] |  |
IPL [Member] | Thereafter [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 886 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember |  |  |
IPL [Member] | Thereafter [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 882 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [1] |  |
IPL [Member] | Thereafter [Member] | DAEC [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 882 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [1],[2] |  |
IPL [Member] | Thereafter [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [1] |  |
IPL [Member] | Thereafter [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 4 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember |  |  |
IPL [Member] | Thereafter [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [3] |  |
IPL [Member] | Thereafter [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [4] |  |
IPL [Member] | Thereafter [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [5] |  |
WPL [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 499 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember |  |  |
WPL [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 207 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember | [1] |  |
WPL [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 125 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember |  |  |
WPL [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 164 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember | [3] |  |
WPL [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 3 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember | [5] |  |
WPL [Member] | 2015 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 206 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember |  |  |
WPL [Member] | 2015 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 74 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [1] |  |
WPL [Member] | 2015 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 67 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember |  |  |
WPL [Member] | 2015 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 63 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [3] |  |
WPL [Member] | 2015 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 2 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueCurrentMember | [5] |  |
WPL [Member] | 2016 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 126 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember |  |  |
WPL [Member] | 2016 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 45 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [1] |  |
WPL [Member] | 2016 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 37 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember |  |  |
WPL [Member] | 2016 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 43 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [3] |  |
WPL [Member] | 2016 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 1 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearTwoMember | [5] |  |
WPL [Member] | 2017 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 89 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember |  |  |
WPL [Member] | 2017 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 44 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [1] |  |
WPL [Member] | 2017 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 18 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember |  |  |
WPL [Member] | 2017 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 27 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [3] |  |
WPL [Member] | 2017 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearThreeMember | [5] |  |
WPL [Member] | 2018 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 70 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember |  |  |
WPL [Member] | 2018 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 44 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [1] |  |
WPL [Member] | 2018 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 3 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember |  |  |
WPL [Member] | 2018 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 23 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [3] |  |
WPL [Member] | 2018 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFourMember | [5] |  |
WPL [Member] | 2019 [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 8 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember |  |  |
WPL [Member] | 2019 [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [1] |  |
WPL [Member] | 2019 [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember |  |  |
WPL [Member] | 2019 [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 8 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [3] |  |
WPL [Member] | 2019 [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueYearFiveMember | [5] |  |
WPL [Member] | Thereafter [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember |  |  |
WPL [Member] | Thereafter [Member] | Purchased Power [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [1] |  |
WPL [Member] | Thereafter [Member] | Natural Gas [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_NaturalGasMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember |  |  |
WPL [Member] | Thereafter [Member] | Coal [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CoalMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [3] |  |
WPL [Member] | Thereafter [Member] | Other [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember / lnt_LongTermPurchaseCommitmentByCategoryPeriodAxis = lnt_LongTermPurchaseCommitmentObligationDueThereafterMember | [5] |  |
Alliant Energy and IPL [Member] | SO2 emission allowances [Member] |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |
Minimum future commitments |  |  |  | $ 34 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_AlliantEnergyAndIplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember
[1] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions.
[2] | Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause.
[3] | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 2014 regarding expected future usage, which is subject to change.
[4] | Refer to Note 2 for discussion of $34 million of charges recognized by Alliant Energy and IPL in 2011 for forward contracts to purchase SO2 emission allowances.
[5] | Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2014.

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