Debt (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2025	Dec. 31, 2023
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000
Payments to retire long-term debt	305	$ 404
Long-term debt, fair value	10,444			$ 8,677
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	450
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	250
Long-term debt, fair value	4,407			3,664
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	300
Long-term debt, fair value	3,322			$ 2,933
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	6.00%
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025 [Member] | Alliant Energy Finance LLC [Member] | Forecast [Member]
Debt [Line Items]
Long-term debt			$ 100
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2024 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Payments to retire long-term debt	$ 300
Senior Notes [Member] | 5.4% senior notes, due 2027 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt	$ 375
Interest rate, percent	5.40%
Senior Debentures [Member] | 4.95% senior debenture, due 2034 [Member] | IPL [Member]
Debt [Line Items]
Long-term debt	$ 350
Interest rate, percent	4.95%
Senior Debentures [Member] | 5.45% senior debenture, due 2054 [Member] | IPL [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	5.45%
Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member] | IPL [Member]
Debt [Line Items]
Long-term debt	$ 500
Interest rate, percent	3.25%
Debentures [Member] | 5.375% debenture, due 2034 [Member] | WPL [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	5.375%
Convertible Senior Notes [Member] | 3.875% convertible senior notes, due 2026 [Member]
Debt [Line Items]
Long-term debt, carrying value	$ 570
Unamortized debt issuance costs	5
Long-term debt, fair value	$ 602
Shares included in diluted earnings per share (in shares)	0