Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Long-term debt		$ 9,925	$ 9,109
Current maturities		(1,171)	(809)
Unamortized debt issuance costs		(55)	(54)
Unamortized debt (discount) and premium, net		(22)	(21)
Long-term debt, net		8,677	8,225
Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt		4,125	3,975
Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		3.40%	3.40%
Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 50	$ 50
Interest rate, percent		5.50%	5.50%
Senior Debentures [Member] | 4.1% senior debenture, due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 500	$ 500
Interest rate, percent		4.10%	4.10%
Senior Debentures [Member] | 3.6% senior debenture, due 2029 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.60%	3.60%
Senior Debentures [Member] | 2.3% senior debenture, due 2030 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 400	$ 400
Interest rate, percent		2.30%	2.30%
Senior Debentures [Member] | 5.7%, senior debentures, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		5.70%	5.70%
Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 100	$ 100
Interest rate, percent		6.45%	6.45%
Senior Debentures [Member] | 4.95% senior debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 350
Interest rate, percent		4.95%
Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 125	$ 125
Interest rate, percent		6.30%	6.30%
Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		6.25%	6.25%
Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		4.70%	4.70%
Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.70%	3.70%
Senior Debentures [Member] | 3.5% senior debenture, due 2049 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.50%	3.50%
Senior Debentures [Member] | 3.1% senior debenture, due 2051 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.10%	3.10%
Senior Debentures [Member] | 5.45% senior debenture, due 2054 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300
Interest rate, percent		5.45%
Senior Debentures [Member] | 3.25% senior debenture, retired in 2024
Debt Instrument [Line Items]
Long-term debt			$ 500
Interest rate, percent			3.25%
Debentures [Member]
Debt Instrument [Line Items]
Long-term debt		$ 3,400	$ 3,100
Debentures [Member] | 3.05% debenture, due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.05%	3.05%
Debentures [Member] | 3% debenture, due 2029 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 350	$ 350
Interest rate, percent		3.00%	3.00%
Debentures [Member] | 1.95% debenture, due 2031 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		1.95%	1.95%
Debentures [Member] | 3.95% debenture, due 2032 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 600	$ 600
Interest rate, percent		3.95%	3.95%
Debentures [Member] | 4.95% debenture, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		4.95%	4.95%
Debentures [Member] | 5.375% debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300
Interest rate, percent		5.375%
Debentures [Member] | 6.25% debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 100	$ 100
Interest rate, percent		6.25%	6.25%
Debentures [Member] | 6.375% debenture, due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		6.375%	6.375%
Debentures [Member] | 7.6% debenture, due 2038 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		7.60%	7.60%
Debentures [Member] | 4.1% debenture, due 2044 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		4.10%	4.10%
Debentures [Member] | 3.65% debenture, due 2050 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 350	$ 350
Interest rate, percent		3.65%	3.65%
Senior Notes [Member] | 3.875% senior notes, due 2026 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 575	$ 575
Interest rate, percent		3.875%	3.875%
Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt		$ 2,400	$ 2,034
IPL [Member]
Debt Instrument [Line Items]
Long-term debt		4,125	3,975
Current maturities		(300)	(500)
Unamortized debt issuance costs		(25)	(21)
Unamortized debt (discount) and premium, net		(10)	(9)
Long-term debt, net		3,790	3,445
IPL [Member] | Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt		4,125	3,975
IPL [Member] | Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		3.40%	3.40%
IPL [Member] | Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 50	$ 50
Interest rate, percent		5.50%	5.50%
IPL [Member] | Senior Debentures [Member] | 4.1% senior debenture, due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 500	$ 500
Interest rate, percent		4.10%	4.10%
IPL [Member] | Senior Debentures [Member] | 3.6% senior debenture, due 2029 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.60%	3.60%
IPL [Member] | Senior Debentures [Member] | 2.3% senior debenture, due 2030 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 400	$ 400
Interest rate, percent		2.30%	2.30%
IPL [Member] | Senior Debentures [Member] | 5.7%, senior debentures, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		5.70%	5.70%
IPL [Member] | Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 100	$ 100
Interest rate, percent		6.45%	6.45%
IPL [Member] | Senior Debentures [Member] | 4.95% senior debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 350
Interest rate, percent		4.95%
IPL [Member] | Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 125	$ 125
Interest rate, percent		6.30%	6.30%
IPL [Member] | Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		6.25%	6.25%
IPL [Member] | Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		4.70%	4.70%
IPL [Member] | Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.70%	3.70%
IPL [Member] | Senior Debentures [Member] | 3.5% senior debenture, due 2049 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.50%	3.50%
IPL [Member] | Senior Debentures [Member] | 3.1% senior debenture, due 2051 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.10%	3.10%
IPL [Member] | Senior Debentures [Member] | 5.45% senior debenture, due 2054 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300
Interest rate, percent		5.45%
IPL [Member] | Senior Debentures [Member] | 3.25% senior debenture, retired in 2024
Debt Instrument [Line Items]
Long-term debt			$ 500
Interest rate, percent			3.25%
WPL [Member]
Debt Instrument [Line Items]
Long-term debt		$ 3,400	$ 3,100
Current maturities		0	0
Unamortized debt issuance costs		(20)	(19)
Unamortized debt (discount) and premium, net		(10)	(11)
Long-term debt, net		3,370	3,070
WPL [Member] | Debentures [Member]
Debt Instrument [Line Items]
Long-term debt		3,400	3,100
WPL [Member] | Debentures [Member] | 3.05% debenture, due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		3.05%	3.05%
WPL [Member] | Debentures [Member] | 3% debenture, due 2029 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 350	$ 350
Interest rate, percent		3.00%	3.00%
WPL [Member] | Debentures [Member] | 1.95% debenture, due 2031 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		1.95%	1.95%
WPL [Member] | Debentures [Member] | 3.95% debenture, due 2032 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 600	$ 600
Interest rate, percent		3.95%	3.95%
WPL [Member] | Debentures [Member] | 4.95% debenture, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		4.95%	4.95%
WPL [Member] | Debentures [Member] | 5.375% debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300
Interest rate, percent		5.375%
WPL [Member] | Debentures [Member] | 6.25% debenture, due 2034 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 100	$ 100
Interest rate, percent		6.25%	6.25%
WPL [Member] | Debentures [Member] | 6.375% debenture, due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		6.375%	6.375%
WPL [Member] | Debentures [Member] | 7.6% debenture, due 2038 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		7.60%	7.60%
WPL [Member] | Debentures [Member] | 4.1% debenture, due 2044 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 250	$ 250
Interest rate, percent		4.10%	4.10%
WPL [Member] | Debentures [Member] | 3.65% debenture, due 2050 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 350	$ 350
Interest rate, percent		3.65%	3.65%
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025, Variable Rate [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300
Interest rate, percent		6.00%
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025, Variable Rate [Member] | Forecast [Member]
Debt Instrument [Line Items]
Long-term debt	$ 100
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement, retired in 2024, Variable Rate [Member]
Debt Instrument [Line Items]
Long-term debt			$ 300
Interest rate, percent			6.00%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 1.4% senior notes, due 2026 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 200	$ 200
Interest rate, percent		1.40%	1.40%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 5.4% senior notes, due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 375
Interest rate, percent		5.40%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 4.25% senior notes, due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		4.25%	4.25%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 5.95% senior notes, due 2029 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 300	$ 300
Interest rate, percent		5.95%	5.95%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 3.6% senior notes, due 2032 [Member]
Debt Instrument [Line Items]
Long-term debt		$ 350	$ 350
Interest rate, percent		3.60%	3.60%
Sheboygan Power, LLC [Member] | Senior Secured Notes [Member] | 5.06% senior secured notes, retired in 2024 [Member]
Debt Instrument [Line Items]
Long-term debt			$ 9
Interest rate, percent			5.06%