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Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | $ 8.7 | $ 6.8 | $ 17.3 | $ 13.2
Income tax rates for continuing operations, production tax credits | (7.90%) | (6.30%) | (7.70%) | (6.60%)
IPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Income tax rates for continuing operations, production tax credits | (10.50%) | (8.60%) | (10.10%) | (8.90%)
WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | 4.6 | 3.7 | 9.3 | 6.5
Income tax rates for continuing operations, production tax credits | (7.20%) | (6.50%) | (7.00%) | (6.40%)
Cedar Ridge Wind Project [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | 1.1 | 1.0 | 2.3 | 2.3
Bent Tree - Phase I Wind Project [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | 3.5 | 2.7 | 7.0 | 4.2
Whispering Willow - East Wind Project [Member] | IPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | $ 4.1 | $ 3.1 | $ 8.0 | $ 6.7

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- Definition The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to the deduction for qualified production activities received under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=6889476&loc=d3e330036-122817 + Details
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