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Callaway Energy Center (Narrative) (Details) - Ameren Missouri - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Nuclear Waste Matters [Line Items]    
Decommissioning Cost   $ 7
Frequency of Decommissioning Cost Study   3 years
Future Decommissioning Cost $ 0  
Minimum | Nuclear Decommissioning Trust Fund    
Nuclear Waste Matters [Line Items]    
Trust Fund Investments, Target Allocation Percentage   60.00%
Maximum | Nuclear Decommissioning Trust Fund    
Nuclear Waste Matters [Line Items]    
Trust Fund Investments, Target Allocation Percentage   70.00%