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Investments
 9 Months Ended
Sep. 30, 2025
Schedule of Equity Method Investments [Line Items]  
Investments INVESTMENTS
Unconsolidated Equity Investments - Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions):
Three MonthsNine Months
2025202420252024
ATC Holdings($15)($13)($43)($38)
Non-utility wind farm in Oklahoma(2)(2)(6)(5)
Corporate venture investments(1)2101
Other—(1)(2)(2)
($18)($14)($41)($44)