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Common Equity (Common Share Activity) (Details) | 3 Months Ended
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Mar. 31, 2015
Common Stock Oustanding [Roll Forward] |
Shares outstanding, January 1, 2015 (in shares) | 110,935,680 us-gaap_CommonStockSharesOutstanding
New shares of stock issued, Shareowner Direct Plan (in shares) | 11,193 lnt_SharesOfStockIssuedShareownerDirectPlan
Equity-based compensation plans (in shares) | 56,378 us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans
Other (in shares) | (22,463)us-gaap_StockIssuedDuringPeriodSharesOther
Shares outstanding, March 31, 2015 (in shares) | 112,977,238 us-gaap_CommonStockSharesOutstanding
At The Market Offering Program [Member] |
Common Stock Oustanding [Roll Forward] |
New shares of common stock issued, At-the-market offering program (in shares) | 1,996,450 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_SubsidiarySaleOfStockAxis = lnt_AtTheMarketOfferingProgramMember

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- Definition Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 30 -Article 5 + Details
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- Definition Number of shares issued during the period as a result of an employee stock purchase plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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