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Common Equity (Schedule Of Restricted Net Assets of Subsidiaries) (Details) (USD $) In Billions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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IPL [Member] |  |
Restricted net assets of subsidiaries | $ 1.3 us-gaap_AmountOfRestrictedNetAssetsForConsolidatedAndUnconsolidatedSubsidiaries / dei_LegalEntityAxis = lnt_IplMember | $ 1.2 us-gaap_AmountOfRestrictedNetAssetsForConsolidatedAndUnconsolidatedSubsidiaries / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |
Restricted net assets of subsidiaries | $ 1.6 us-gaap_AmountOfRestrictedNetAssetsForConsolidatedAndUnconsolidatedSubsidiaries / dei_LegalEntityAxis = lnt_WplMember | $ 1.5 us-gaap_AmountOfRestrictedNetAssetsForConsolidatedAndUnconsolidatedSubsidiaries / dei_LegalEntityAxis = lnt_WplMember

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- Definition Amount of restricted net assets of consolidated and unconsolidated subsidiaries as of the end of the most recently completed fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(e)(3)(ii)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph e -Subparagraph 3 -Article 4 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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