v2.4.0.6

Receivables (Narrative) (Details) (IPL [Member], USD $) In Millions, unless otherwise specified |  |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2012 | Dec. 31, 2011 | Sep. 30, 2012 Maximum [Member] | Sep. 30, 2011 Maximum [Member] | Sep. 30, 2012 Maximum [Member] | Sep. 30, 2011 Maximum [Member] | Sep. 30, 2012 Maximum [Member] March 2012 Through March 2014 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |  |  |
Cash proceeds to be received from third-party |  |  | $ 150.0 | $ 160.0 | $ 160.0 | $ 160.0 | $ 180.0
Receivables sold | $ 210.9 | $ 195.3 |  |  |  |  |

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- Definition Receivables sold + References No definition available. + Details
Name: | lnt_ReceivablesSold
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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- Definition The cash inflow associated with the proceeds from sale and collection of receivables during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 16 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromSaleAndCollectionOfReceivables
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration