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Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) (IPL [Member], USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2013 | Sep. 30, 2012 | Sep. 30, 2013 | Sep. 30, 2012
IPL [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Collections reinvested in receivables | $ 481.1 | $ 522.9 | $ 1,407.4 | $ 1,334.7
Credit losses, net of recoveries | $ 3.9 | $ 3.0 | $ 7.8 | $ 7.3

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- Definition Collections reinvested related to sales of accounts receivable program. + References No definition available. + Details
Name: | lnt_CollectionsReinvestedInReceivables
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Credit losses, net of recoveries related to sales of accounts receivable program. + References No definition available. + Details
Name: | lnt_CreditLossesNetOfRecoveries
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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