Debt (Narrative) (Details)	9 Months Ended
	Sep. 30, 2023 USD ($) Integer $ / shares shares	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000,000,000
Payments to retire long-term debt	404,000,000	$ 379,000,000
Long-term debt, fair value	7,863,000,000		$ 7,339,000,000
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	450,000,000
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	250,000,000
Long-term debt, fair value	3,422,000,000		3,228,000,000
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	300,000,000
Long-term debt, fair value	2,722,000,000		$ 2,542,000,000
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2024 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt	50,000,000
Senior Debentures [Member] | 5.70% senior debenture, due 2033 | IPL [Member]
Debt [Line Items]
Long-term debt	$ 300,000,000
Interest rate, percent	5.70%
Senior Notes [Member] | 3.75% senior notes, due 2023 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Payments to retire long-term debt	$ 400,000,000
Interest rate, percent	3.75%
Debentures [Member] | 4.95% debenture, due 2033 [Member] | WPL [Member]
Debt [Line Items]
Long-term debt	$ 300,000,000
Interest rate, percent	4.95%
Convertible Senior Notes [Member]
Debt [Line Items]
Trading days | Integer	20
Trading days consecutive | Integer	30
Convertible Senior Notes [Member] | 3.875% convertible senior notes, due 2026 [Member]
Debt [Line Items]
Long-term debt	$ 575,000,000
Interest rate, percent	3.875%
Trading days | Integer	5
Trading days consecutive | Integer	10
Principal amount of Notes conversion rate applied to	$ 1,000
Initial conversion ratio	15.5461
Initial conversion price | $ / shares	$ 64.32
Fundamental change repurchase conversion price, percent	100.00%
Long-term debt, carrying value	$ 567,000,000
Unamortized debt issuance costs	8,000,000
Long-term debt, fair value	$ 556,000,000
Shares included in diluted earnings per share (in shares) | shares	0
Convertible Senior Notes [Member] | 3.875% convertible senior notes, due 2026 [Member] | Maximum [Member]
Debt [Line Items]
Conversion price, percent	130.00%
Convertible Senior Notes [Member] | 3.875% convertible senior notes, due 2026 [Member] | Minimum [Member]
Debt [Line Items]
Conversion price, percent	98.00%