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Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended
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Sep. 30, 2014
Commitments and Contingencies [Line Items] |
Minimum future commitments | $ 2,438
Performance guarantees outstanding | 313
Present value abandonment obligation | 31
IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 1,922
Number of sites monitoring and remediating (in sites) | 26
WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 514
Number of sites monitoring and remediating (in sites) | 5
Capital Purchase Obligation [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 45
Capital Purchase Obligation [Member] | IPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 26
Capital Purchase Obligation [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Minimum future commitments | 19
Performance guarantees outstanding, 2014 [Member] |
Commitments and Contingencies [Line Items] |
Performance guarantees outstanding | 137
Performance guarantees outstanding, 2015 [Member] |
Commitments and Contingencies [Line Items] |
Performance guarantees outstanding | 53
Performance guarantees outstanding, 2016 [Member] |
Commitments and Contingencies [Line Items] |
Performance guarantees outstanding | 123
Environmental Issue [Member] | WPL [Member] |
Commitments and Contingencies [Line Items] |
Environmental mitigation projects to be completed, value | $ 7
Minimum [Member] |
Commitments and Contingencies [Line Items] |
Warranty period | 12 months
Maximum [Member] |
Commitments and Contingencies [Line Items] |
Warranty period | 60 months

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- Definition Number of sites remediating and monitoring + References No definition available. + Details
Name: | lnt_Numberofsitesremediatingandmonitoring
Namespace Prefix: | lnt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Performance Guarantees Outstanding + References No definition available. + Details
Name: | lnt_PerformanceGuaranteesOutstanding
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- 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

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- Definition Warranty Period + References No definition available. + Details
Name: | lnt_WarrantyPeriod
Namespace Prefix: | lnt_
Data Type: | xbrli:durationItemType
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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- 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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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration