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Commitments And Contingencies (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 2,270
Present value abandonment obligation	32
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	1,727
Maximum indemnification limit	17
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	543
Capital Purchase Obligation [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	53
Capital Purchase Obligation [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	4
Capital Purchase Obligation [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	49
Environmental Issue [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	6
Environmental Issue [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Environmental mitigation projects to be completed, value	$ 7

X

- Definition

Present value abandonment obligation

+ References

No definition available.

+ Details

Name:	lnt_PresentValueAbandonmentObligation
Namespace Prefix:	lnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- 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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

- 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

X

- Definition

Amount of damages awarded to the plaintiff in the legal matter.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_CapitalPurchaseObligationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LitigationCaseAxis=us-gaap_EnvironmentalIssueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: