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Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Derivative Instruments [Line Items]
Non-current interest rate derivative assets	$ 173		$ 177
Accumulated other comprehensive income, interest rate swap	2		$ 1
Interest expense, interest rate swap	107	$ 94
Alliant Energy Finance LLC [Member] \| Interest Rate Swap [Member] \| Term Loan Credit Agreement [Member]
Derivative Instruments [Line Items]
Non-current interest rate derivative assets	3
Accumulated other comprehensive income, interest rate swap	2
Interest expense, interest rate swap	$ 1	$ 1

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

Amount of the cost of borrowed funds accounted for as interest expense.