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v3.25.3

Commitments And Contingencies (Narrative) (Details) $ in Millions | 9 Months Ended
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Sep. 30, 2025 USD ($)
Commitments and Contingencies [Line Items] |
Minimum future commitments | $ 1,138
IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 593
WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 513
Indemnification Agreement [Member] |
Commitments and Contingencies [Line Items] |
Obligations, maximum | $ 35
Whiting Petroleum Affiliate [Member] |
Commitments and Contingencies [Line Items] |
Partnership share, percent | 6.00%
Obligations, maximum | $ 54
Capital Purchase Commitment [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 332
Capital Purchase Commitment [Member] | IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 136
Capital Purchase Commitment [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 193
Purchased Power [Member] | Indemnification Agreement [Member] |
Commitments and Contingencies [Line Items] |
Obligations, maximum | 17
Renewable Tax Credits Transferred [Member] | Indemnification Agreement [Member] | IPL [Member] |
Commitments and Contingencies [Line Items] |
Obligations, maximum | 283
Renewable Tax Credits Transferred [Member] | Indemnification Agreement [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Obligations, maximum | 148
Reimbursement of Transmission Construction Costs [Member] | Indemnification Agreement [Member] | IPL [Member] |
Commitments and Contingencies [Line Items] |
Obligations, maximum | 35
Reimbursement of Transmission Construction Costs [Member] | Indemnification Agreement [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Obligations, maximum | $ 44

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- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 460 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482425/460-10-50-4 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482987/272-10-50-3 + Details
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Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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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
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |