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Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Derivative Instruments [Line Items]
Non-current interest rate derivative liabilities	$ 939		$ 939		$ 617
Accumulated other comprehensive loss, interest rate swap	1		1		$ (1)
Alliant Energy Finance LLC [Member] \| Interest Rate Swap [Member] \| Term Loan Credit Agreement [Member]
Derivative Instruments [Line Items]
Non-current interest rate derivative liabilities	1		1
Accumulated other comprehensive loss, interest rate swap	1		1
Interest expense, interest rate swap	$ 1	$ 1	$ 3	$ 2

- Definition

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

+ References + Details

- Definition

Amount of interest expense classified as operating and nonoperating. Includes, but is not limited to, cost of borrowing accounted for as interest expense.

+ References + Details