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Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | $ 1,451.0 | $ 1,493.2
Tax-related [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 851.4 | 890.6
Cost of removal obligations [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 390.9 | 401.2
Electric transmission cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 89.8 | 104.0
Commodity cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 29.1 | 16.8
WPL's earnings sharing mechanism [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 21.8 | 25.4
Derivatives [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 20.8 | 18.5
Other [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 47.2 | 36.7
IPL [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 733.6 | 754.9
IPL [Member] | Tax-related [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 365.0 | 390.1
IPL [Member] | Cost of removal obligations [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 261.0 | 273.3
IPL [Member] | Electric transmission cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 48.0 | 47.7
IPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 16.7 | 11.9
IPL [Member] | Derivatives [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 16.9 | 10.2
IPL [Member] | Other [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 26.0 | 21.7
WPL [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 717.4 | 738.3
WPL [Member] | Tax-related [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 486.4 | 500.5
WPL [Member] | Cost of removal obligations [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 129.9 | 127.9
WPL [Member] | Electric transmission cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 41.8 | 56.3
WPL [Member] | Commodity cost recovery [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 12.4 | 4.9
WPL [Member] | WPL's earnings sharing mechanism [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 21.8 | 25.4
WPL [Member] | Derivatives [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | 3.9 | 8.3
WPL [Member] | Other [Member] |  |
Regulatory Liabilities [Line Items] |  |
Regulatory liabilities | $ 21.2 | $ 15.0

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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://fasb.org/us-gaap/role/ref/legacyRef -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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