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Derivative Instruments (Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments) (Details) (Commodity Contracts [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Regulatory Assets [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains (losses) from derivative instruments not designated as heding instruments | $ (14.7) | $ (37.9) | $ (79.6)
Regulatory Assets [Member] | IPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains (losses) from derivative instruments not designated as heding instruments | (6.6) | (16.8) | (42.4)
Regulatory Assets [Member] | WPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains (losses) from derivative instruments not designated as heding instruments | (8.1) | (21.1) | (37.2)
Regulatory Liabilities [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains (losses) from derivative instruments not designated as heding instruments | 22.2 | 20.3 | 9.3
Regulatory Liabilities [Member] | IPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains (losses) from derivative instruments not designated as heding instruments | 11.8 | 13.5 | 6.4
Regulatory Liabilities [Member] | WPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Gains (losses) from derivative instruments not designated as heding instruments | $ 10.4 | $ 6.8 | $ 2.9

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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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