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Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | $ 2,283 us-gaap_LongTermPurchaseCommitmentAmount |
Individual commitments incurred | 1 lnt_IndividualCommitmentsIncurred |
IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 1,795 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember |
WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 488 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember |
DAEC (IPL) [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 1,510 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember | [1]
DAEC (IPL) [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 1,510 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember | [1]
DAEC (IPL) [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember | [1]
Other [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 220 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember | [1]
Other [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 1 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember | [1]
Other [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 219 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerOtherMember | [1]
Purchased Power [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 1,730 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember | [1]
Purchased Power [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 1,511 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember | [1]
Purchased Power [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 219 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_PurchasedPowerMember | [1]
Natural Gas [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 228 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_PublicUtilitiesInventoryNaturalGasMember |
Natural Gas [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 120 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_PublicUtilitiesInventoryNaturalGasMember |
Natural Gas [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 108 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_PublicUtilitiesInventoryNaturalGasMember |
Coal [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 264 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_CoalSupplyAgreementsMember | [2]
Coal [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 113 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_CoalSupplyAgreementsMember | [2]
Coal [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 151 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = us-gaap_CoalSupplyAgreementsMember | [2]
SO2 emission allowances [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 22 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember |
SO2 emission allowances [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 22 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember |
SO2 emission allowances [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 0 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_So2EmissionAllowancesMember |
Other [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 39 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember | [3]
Other [Member] | IPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | 29 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember | [3]
Other [Member] | WPL [Member] |  |
Commitments and Contingencies [Line Items] |  |
Minimum future commitments | $ 10 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_LongTermPurchaseCommitmentsOtherMember | [3]
[1] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
[2] | 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 March 31, 2015 regarding expected future usage, which is subject to change.
[3] | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2015.

X
- Definition Individual commitments incurred in excess of $1 million + References No definition available. + Details
Name: | lnt_IndividualCommitmentsIncurred
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The minimum amount the entity agreed to spend under the long-term purchase commitment. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentLineItems
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_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_DaecIplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_LongTermPurchaseCommitmentsOtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_PurchasedPowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_PurchasedPowerOtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_So2EmissionAllowancesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=us-gaap_CoalSupplyAgreementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=us-gaap_PublicUtilitiesInventoryNaturalGasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |