Electric Capacity Of Wind Project

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Reduction In Equity Due To Investment Transfer

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
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-Section 45
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The net cash outflow or inflow for net proceeds and payments derived from carrying life insurance policies for which the entity is the beneficiary.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

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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.

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Investments (Narrative) (Details) $ in Millions	1 Months Ended	12 Months Ended
Investments (Narrative) (Details) $ in Millions	Jul. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) MW	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Carrying value		$ 381.4	$ 326.0	$ 302.9
Proceeds from liquidation of company-owned life insurance policies			31.0
WPL [Member]
Schedule of Equity Method Investments [Line Items]
WPL's ownership interest in WPL Transco					100.00%
Net reduction in total equity due to transfer of ATC investment to ATI			163.6
IPL [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from liquidation of company-owned life insurance policies			$ 19.0
Alliant Energy Finance, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest		50.00%
Electric capacity of wind farm (in megawatts) \| MW		225
Carrying value		$ 98.0
Term Loan Credit Agreement [Member] \| Alliant Energy Finance, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from the issuance of debt	$ 95.0
Variable-rate term loan credit agreement, period	364 days