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v2.4.1.9

Segments Of Business (Schedule Of Segments Of Business) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Segment Reporting Information [Line Items] |  |
Operating revenues | $ 897.4 us-gaap_Revenues | $ 952.8 us-gaap_Revenues
Operating income (loss) | 152.9 us-gaap_OperatingIncomeLoss | 154.2 us-gaap_OperatingIncomeLoss
Net income (loss) attributable to common shareowners | 96.6 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 108.0 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 489.0 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember | 528.9 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember
Operating income (loss) | 65.5 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember | 57.5 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember
Net income (loss) attributable to common shareowners | 47.8 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember | 43.4 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 397.1 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember | 410.4 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember
Operating income (loss) | 80.8 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember | 87.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember
Net income (loss) attributable to common shareowners | 44.6 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember | 54.8 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / dei_LegalEntityAxis = lnt_WplMember
Electric [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 671.3 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 675.8 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember
Operating income (loss) | 104.7 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 94.3 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember
Electric [Member] | IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 362.6 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 374.2 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember
Operating income (loss) | 40.3 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 26.5 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember
Electric [Member] | WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 308.7 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 301.6 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember
Operating income (loss) | 64.4 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 67.8 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember
Gas [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 198.4 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 240.7 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember
Operating income (loss) | 36.3 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 43.0 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember
Gas [Member] | IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 111.2 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 135.7 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember
Operating income (loss) | 20.6 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 23.3 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember
Gas [Member] | WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 87.2 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 105.0 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember
Operating income (loss) | 15.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 19.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember
Other Utilities [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 16.4 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 22.8 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember
Operating income (loss) | 5.3 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 7.9 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember
Other Utilities [Member] | IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 15.2 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 19.0 us-gaap_Revenues / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember
Operating income (loss) | 4.6 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 7.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_IplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember
Other Utilities [Member] | WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 1.2 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 3.8 us-gaap_Revenues / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember
Operating income (loss) | 0.7 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 0.2 us-gaap_OperatingIncomeLoss / dei_LegalEntityAxis = lnt_WplMember / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember
Utilities Business [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 886.1 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_UtilityBusinessMember | 939.3 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = lnt_UtilityBusinessMember
Operating income (loss) | 146.3 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_UtilityBusinessMember | 145.2 us-gaap_OperatingIncomeLoss / us-gaap_StatementBusinessSegmentsAxis = lnt_UtilityBusinessMember
Net income (loss) attributable to common shareowners | 92.4 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = lnt_UtilityBusinessMember | 98.2 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_StatementBusinessSegmentsAxis = lnt_UtilityBusinessMember
Non-Regulated [Member] | Other Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Operating revenues | 11.3 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | 13.5 us-gaap_Revenues / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember
Operating income (loss) | 6.6 us-gaap_OperatingIncomeLoss / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | 9.0 us-gaap_OperatingIncomeLoss / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember
Net income (loss) attributable to common shareowners | $ 4.2 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | $ 9.8 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis = us-gaap_UnregulatedOperationMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember

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