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Derivative Instruments (Gains And Losses From Derivative Instruments) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended
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Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013
Regulatory Assets [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) from commodity derivative instruments | $ (4.6) | $ (25.9) | $ 5.5 | $ (16.4)
Regulatory Assets [Member] | IPL [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) from commodity derivative instruments | (4.1) | (6.9) | 1.4 | (4.2)
Regulatory Assets [Member] | WPL [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) from commodity derivative instruments | (0.5) | (19.0) | 4.1 | (12.2)
Regulatory Liabilities [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) from commodity derivative instruments | 21.3 | 1.2 | 69.4 | 17.6
Regulatory Liabilities [Member] | IPL [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) from commodity derivative instruments | 3.8 | (2.5) | 15.9 | 6.3
Regulatory Liabilities [Member] | WPL [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) from commodity derivative instruments | $ 17.5 | $ 3.7 | $ 53.5 | $ 11.3

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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=35706170&loc=SL5624171-113959 + Details
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