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v3.20.2

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions | 9 Months Ended
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Sep. 30, 2020 USD ($)
Commitments and Contingencies [Line Items] |
Minimum future commitments | $ 1,219
Individual commitments incurred | 1
IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 627
Individual commitments incurred | 1
WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 561
Individual commitments incurred | 1
Natural gas [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 983
Natural gas [Member] | IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 508
Natural gas [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 475
Coal [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 125
Coal [Member] | IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 70
Coal [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 55
Other [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 111
Other [Member] | IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 49
Other [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | $ 31

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- 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

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- 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

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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

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

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

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