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Investments (Tables)
 3 Months Ended
Mar. 31, 2024
Schedule of Equity Method Investments [Line Items]  
Unconsolidated Equity Investments Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):
20242023
ATC Holdings($12)($13)
Other(3)(4)
($15)($17)