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Segments Of Business (Products And Services) (Details) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Segment Reporting Information [Line Items] |  |  |
Products and services | 100.00%us-gaap_ConcentrationRiskPercentage1 | 100.00%us-gaap_ConcentrationRiskPercentage1 | 100.00%us-gaap_ConcentrationRiskPercentage1
Utility electric operations [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Products and services | 81.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 82.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember | 84.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_ElectricMember
Utility gas operations [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Products and services | 15.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 14.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember | 13.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_GasMember
Utility other [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Products and services | 2.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 2.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember | 2.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = lnt_OtherUtilityMember
Other [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Products and services | 2.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | 2.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember | 1.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_StatementBusinessSegmentsAxis = us-gaap_AllOtherSegmentsMember

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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592 + Details
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- Details
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- Details
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Period Type: |

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

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- Details
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Balance Type: |
Period Type: |

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- Details
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