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Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions | Jun. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | $ 665.8 | $ 681.0
Cost of removal obligations [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 415.3 | 411.6
Electric transmission cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 118.5 | 72.0
IPL's tax benefit riders [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 47.2 | 83.5
Commodity cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 27.5 | 30.8
Energy efficiency cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 19.6 | 20.5
Derivatives [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 11.4 | 31.5
Other [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 26.3 | 31.1
IPL [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 415.7 | 430.8
IPL [Member] | Cost of removal obligations [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 273.0 | 269.4
IPL [Member] | Electric transmission cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 61.7 | 35.7
IPL [Member] | IPL's tax benefit riders [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 47.2 | 83.5
IPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 15.9 | 17.8
IPL [Member] | Derivatives [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 7.1 | 12.1
IPL [Member] | Other [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 10.8 | 12.3
WPL [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 250.1 | 250.2
WPL [Member] | Cost of removal obligations [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 142.3 | 142.2
WPL [Member] | Electric transmission cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 56.8 | 36.3
WPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 11.6 | 13.0
WPL [Member] | Energy efficiency cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 19.6 | 20.5
WPL [Member] | Derivatives [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 4.3 | 19.4
WPL [Member] | Other [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | $ 15.5 | $ 18.8

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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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