Commitments And Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
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

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.

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

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPMembersOrLimitedPartnersOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- 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

- 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

- Details

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

- Details

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

- Details

Name:	us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_IndemnificationGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=lnt_WhitingPetroleumCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_RenewableTaxCreditsTransferredMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=lnt_ReimbursementOfTransmissionConstructionCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: