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Receivables (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2014 | Mar. 31, 2015 | Dec. 31, 2014
Receivables [Line Items] |  |  |  |  |
Deferred proceeds |  | $ 117.7 lnt_FairValueOfDeferredProceedsOfReceivablesSold |  | $ 177.2 lnt_FairValueOfDeferredProceedsOfReceivablesSold |
IPL [Member] |  |  |  |  |
Receivables [Line Items] |  |  |  |  |
Receivables sold to third party |  | 197.5 lnt_ReceivablesSold / dei_LegalEntityAxis = lnt_IplMember |  |  |
Deferred proceeds |  | 117.7 lnt_FairValueOfDeferredProceedsOfReceivablesSold / dei_LegalEntityAxis = lnt_IplMember |  | 177.2 lnt_FairValueOfDeferredProceedsOfReceivablesSold / dei_LegalEntityAxis = lnt_IplMember |
Whiting Petroleum Corporation [Member] |  |  |  |  |
Receivables [Line Items] |  |  |  |  |
Final payment of certain future tax benefits expected to be realized | 26 us-gaap_ProceedsFromCollectionOfOtherReceivables / dei_LegalEntityAxis = lnt_WhitingPetroleumCorporationMember |  |  |  |
Receivables Sold [Member] | IPL [Member] |  |  |  |  |
Receivables [Line Items] |  |  |  |  |
Receivables sold to third party |  | 197.5 lnt_ReceivablesSold / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = lnt_ReceivablesSoldMember / dei_LegalEntityAxis = lnt_IplMember |  | 204.6 lnt_ReceivablesSold / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = lnt_ReceivablesSoldMember / dei_LegalEntityAxis = lnt_IplMember |
Cash proceeds of receivables sold |  | 74.0 lnt_CashProceedsFromReceivablesSold / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = lnt_ReceivablesSoldMember / dei_LegalEntityAxis = lnt_IplMember | [1] | 22.0 lnt_CashProceedsFromReceivablesSold / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = lnt_ReceivablesSoldMember / dei_LegalEntityAxis = lnt_IplMember | [1]
Deferred proceeds |  | $ 117.7 lnt_FairValueOfDeferredProceedsOfReceivablesSold / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = lnt_ReceivablesSoldMember / dei_LegalEntityAxis = lnt_IplMember |  | $ 177.2 lnt_FairValueOfDeferredProceedsOfReceivablesSold / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = lnt_ReceivablesSoldMember / dei_LegalEntityAxis = lnt_IplMember |
[1] | Changes in cash proceeds are presented in “Sales of accounts receivable” in operating activities in Alliant Energy’s and IPL’s cash flows statements.

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- Definition Cash Proceeds From Receivables Sold + References No definition available. + Details
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- Definition Fair value of deferred proceeds of receivables sold + References No definition available. + Details
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- Definition Receivables sold + References No definition available. + Details
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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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