Contractual interest rate for funds borrowed, under the debt agreement.

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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
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The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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Debt (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
Debt (Narrative) (Details) - USD ($) $ in Millions	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2019
Debt [Line Items]
Payments to retire long-term debt			$ 300.3	$ 0.3
Term Loan Credit Agreement [Member] \| Term Loan Credit Agreement Through March 2022 [Member] \| Alliant Energy Finance, LLC [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt		$ 300.0
Interest rate, percent		1.00%	1.00%
Term Loan Credit Agreement [Member] \| Term Loan Credit Agreement Through April 2020 [Member] \| Alliant Energy Finance, LLC [Member]
Debt [Line Items]
Payments to retire long-term debt		$ 300.0
Subsequent Event [Member] \| Debentures [Member] \| 3.65% debenture, due 2050 [Member] \| WPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt	$ 350.0
Interest rate, percent	3.65%