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Debt (Narrative) (Details) - USD ($) | 1 Months Ended |  |
--- | --- | --- | ---
Jul. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017
Debt Instrument [Line Items] |  |  |
Line of credit facility, current borrowing capacity |  |  | $ 1,000,000,000
Non-recourse debt and hybrid securities consolidated capital maximum limit |  |  | 15.00%
Parent Company [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, current borrowing capacity |  |  | $ 400,000,000
IPL [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, current borrowing capacity |  |  | 250,000,000
WPL [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, current borrowing capacity |  |  | $ 350,000,000
Scenario, Forecast [Member] | Parent Company [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 500,000,000 |
Scenario, Forecast [Member] | IPL [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, maximum borrowing capacity |  | 400,000,000 |
Scenario, Forecast [Member] | WPL [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 500,000,000 |
Term Loan Credit Agreement [Member] | Alliant Energy Finance, LLC [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Proceeds from the issuance of debt | $ 95,000,000 |  |
Variable-rate term loan credit agreement, period | 364 days |  |
Interest rate |  |  | 2.20%

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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