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

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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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-Publisher FASB
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-Topic 230
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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			6 Months Ended
Debt (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Apr. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019
Debt [Line Items]
Payments to retire long-term debt				$ 653.7	$ 3.4
IPL [Member]
Debt [Line Items]
Payments to retire long-term debt				200.0	0.0
WPL [Member]
Debt [Line Items]
Payments to retire long-term debt				$ 150.0	$ 0.0
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
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%
Debentures [Member] \| 4.6% debenture, due 2020 [Member] \| WPL [Member]
Debt [Line Items]
Interest rate, percent	4.60%			4.60%
Payments to retire long-term debt	$ 150.0
Senior Debentures [Member] \| 2.3% senior debenture, due 2030 [Member] \| IPL [Member]
Debt [Line Items]
Proceeds from issuance of long-term debt	$ 400.0
Interest rate, percent	2.30%			2.30%
Senior Debentures [Member] \| 3.65% senior debenture, due 2020 [Member] \| IPL [Member]
Debt [Line Items]
Interest rate, percent	3.65%			3.65%
Payments to retire long-term debt	$ 200.0