Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Derivative Instruments [Line Items]
Non-current interest rate swap liabilities	$ 540		$ 518
Accumulated other comprehensive loss, interest rate swap	(1)		$ 0
Interest expense, interest rate swap	94	$ 74
Alliant Energy Finance LLC [Member] \| Interest Rate Swap [Member] \| Term Loan Credit Agreement [Member]
Derivative Instruments [Line Items]
Interest rate swap	$ 300
Interest rate swap, fixed interest rate percentage	3.93%
Non-current interest rate swap liabilities	$ 1
Accumulated other comprehensive loss, interest rate swap	1
Interest expense, interest rate swap	$ 1

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

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