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Investments
 3 Months Ended
Mar. 31, 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 months ended March 31 was as follows (in millions):
20252024
ATC Holdings($14)($12)
Other1(3)
($13)($15)