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Receivables (Narrative) (Details) (USD $) In Millions, unless otherwise specified |  |  | 3 Months Ended
--- | --- | --- | ---
Mar. 31, 2014 IPL [Member] | Dec. 31, 2013 IPL [Member] | Mar. 31, 2014 Whiting Petroleum Corporation [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Receivables sold | $ 251.6 | $ 238.0 |
Final payment of certain future tax benefits expected to be realized |  |  | $ 26

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

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- Details
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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 collection of other receivables not otherwise defined in the taxonomy. + References Reference 1: 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=31042434&loc=d3e3179-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration