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Property, Plant and Equipment (AFUDC By Project) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | $ 36.9 | $ 34.8 | $ 30.8
IPL [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 28.2 | 25.9 | 21.0
IPL [Member] | Marshalltown Generating Station [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 20.7 | 3.7 | 0.0
IPL [Member] | Ottumwa Unit 1 [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 0.0 | 10.6 | 8.0
IPL [Member] | George Neal Units 3 and 4 [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 0.0 | 1.4 | 5.1
IPL [Member] | Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 7.5 | 10.2 | 7.9
WPL [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 8.7 | 8.9 | 9.8
WPL [Member] | Edgewater Unit 5 [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 5.1 | 2.7 | 0.0
WPL [Member] | Columbia Units 1 and 2 [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | 0.0 | 4.0 | 7.2
WPL [Member] | Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Allowance for funds used during construction | $ 3.6 | $ 2.2 | $ 2.6

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- Definition Total increase in earnings in the period representing the cost of equity (based on assumed rate of return) and/or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44278-110382 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500269&loc=d3e45485-110386 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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