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Regulatory Matters (IPL's Tax Benefit Riders) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Regulatory Assets [Line Items] |  |  |
Increase (decrease) in regulatory liabilities | $ (67.8) | $ 10.8 | $ (90.8)
Alliant Energy and IPL [Member] | Electric tax benefit rider credits [Member] |  |  |
Regulatory Assets [Line Items] |  |  |
Increase (decrease) in regulatory liabilities | (72.0) |  |
Alliant Energy and IPL [Member] | Gas tax benefit rider credits [Member] |  |  |
Regulatory Assets [Line Items] |  |  |
Increase (decrease) in regulatory liabilities | (12.0) |  |
Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member] |  |  |
Regulatory Assets [Line Items] |  |  |
Increase (decrease) in regulatory liabilities | $ (84.0) |  |

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- Definition The increase (decrease) during the reporting period in regulated liabilities. Regulated liabilities are created when regulatory agency permits an entity to defer revenues to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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