Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Derivative Instruments [Line Items]
Non-current interest rate swap liabilities	$ 544		$ 544		$ 518
Accumulated other comprehensive income, interest rate swap	4		4		$ 0
Interest expense, interest rate swap	99	$ 83	289	$ 235
Alliant Energy Finance LLC [Member] \| Interest Rate Swap [Member] \| Term Loan Credit Agreement [Member]
Derivative Instruments [Line Items]
Interest rate swap	$ 300		$ 300
Interest rate swap, fixed interest rate percentage	3.93%		3.93%
Non-current interest rate swap liabilities	$ 6		$ 6
Accumulated other comprehensive income, interest rate swap	4		4
Interest expense, interest rate swap	$ 1		$ 2

Amount, after tax, of accumulated increase (decrease) in equity from transaction and other event and circumstance from nonowner source.

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Fixed interest rate related to the interest rate derivative.

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