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v2.4.1.9

Common Equity (Capital Transactions With Subsidiaries) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Common stock dividends | $ 225.8 us-gaap_PaymentsOfDividendsCommonStock | $ 208.3 us-gaap_PaymentsOfDividendsCommonStock | $ 199.3 us-gaap_PaymentsOfDividendsCommonStock
IPL [Member] |  |  |
Common stock dividends | 140.0 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_IplMember | 128.1 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_IplMember | 122.9 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_IplMember
Repayments of capital | 0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_IplMember | 0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_IplMember
Total distributions from common equity | 140.0 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_IplMember | 128.1 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_IplMember | 122.9 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |  |
Common stock dividends | 118.7 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_WplMember | 116.3 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_WplMember | 112.0 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_WplMember
Repayments of capital | 0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_WplMember | 0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_WplMember | 0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_WplMember
Total distributions from common equity | 118.7 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_WplMember | 116.3 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_WplMember | 112.0 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_WplMember
Resources [Member] |  |  |
Common stock dividends | 0 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_ResourcesMember | 0 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_ResourcesMember | 0 us-gaap_PaymentsOfDividendsCommonStock / dei_LegalEntityAxis = lnt_ResourcesMember
Repayments of capital | 50.0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_ResourcesMember | 95.0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_ResourcesMember | 0 us-gaap_PaymentsOfCapitalDistribution / dei_LegalEntityAxis = lnt_ResourcesMember
Total distributions from common equity | $ 50.0 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_ResourcesMember | $ 95.0 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_ResourcesMember | $ 0 us-gaap_PaymentsOfDistributionsToAffiliates / dei_LegalEntityAxis = lnt_ResourcesMember

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- Definition Cash outflow to owners or shareholders, excluding ordinary dividends. Includes special dividends. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 + Details
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- Definition The distributions of earnings to an entity that is affiliated with the reporting entity by means of direct or indirect ownership. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 + Details
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- Definition Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585 + Details
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