v2.4.0.6

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, 2012 | Sep. 30, 2011 | Sep. 30, 2012 | Sep. 30, 2011
IPL [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Collections reinvested in receivables | $ 522.9 | $ 482.3 | $ 1,334.7 | $ 1,367.8
Credit losses, net of recoveries | $ 3.0 | $ 3.4 | $ 7.3 | $ 7.9

X
- 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

X
- 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

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