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Derivative Instruments (Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2014 | Mar. 31, 2013
Regulatory Assets [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gains (losses) from commodity derivative instruments not designated as hedging instruments | $ 10.1 | $ 9.5
Regulatory Assets [Member] | IPL [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gains (losses) from commodity derivative instruments not designated as hedging instruments | 5.5 | 2.7
Regulatory Assets [Member] | WPL [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gains (losses) from commodity derivative instruments not designated as hedging instruments | 4.6 | 6.8
Regulatory Liabilities [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gains (losses) from commodity derivative instruments not designated as hedging instruments | 48.1 | 16.4
Regulatory Liabilities [Member] | IPL [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gains (losses) from commodity derivative instruments not designated as hedging instruments | 12.1 | 8.8
Regulatory Liabilities [Member] | WPL [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gains (losses) from commodity derivative instruments not designated as hedging instruments | $ 36.0 | $ 7.6

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- Definition Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959 + Details
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