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Commitments And Contingencies (Environmental Matters) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2025
USD ($)
energyCenter
scrubber
site
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Other current liabilities $ 570 $ 475  
Other deferred credits and liabilities 540 487  
Other operations and maintenance 1,974 1,969 $ 1,866
Asset Retirement Obligation $ 854 827 791
Environmental Loss Contingency Statement Of Financial Position Extensible Enumeration Not Disclosed Flag false    
Rush Island Energy Center Additional Mitigation Relief Ordered      
Other current liabilities $ 36 40  
Other deferred credits and liabilities   24  
Other operations and maintenance   59  
Ameren Missouri      
Number of Energy Center Scrubbers | scrubber 2    
Other current liabilities $ 212 235  
Other deferred credits and liabilities 184 150  
Other operations and maintenance 1,029 1,050 1,003
Asset Retirement Obligation $ 849 823 787
Number of Ameren Missouri Natural Gas Energy Centers Subject To IETL | energyCenter 4    
Ameren Missouri | Rush Island Energy Center Additional Mitigation Relief Ordered      
Other current liabilities $ 36 40  
Other deferred credits and liabilities   24  
Other operations and maintenance   59  
Ameren Illinois      
Other current liabilities 227 172  
Other deferred credits and liabilities 268 273  
Other operations and maintenance 945 906 818
Asset Retirement Obligation $ 5 $ 4 $ 4
Number of remediation sites | site 3    
Manufactured Gas Plant      
Accrual for environmental loss contingencies $ 45    
Manufactured Gas Plant | Ameren Illinois      
Number of remediation sites | site 44    
Accrual for environmental loss contingencies $ 45    
Minimum      
Estimated capital costs to comply with existing and known federal and state air emissions regulations 70    
Minimum | Ameren Missouri      
Estimated capital costs to comply with existing and known federal and state air emissions regulations 70    
Minimum | Manufactured Gas Plant | Ameren Illinois      
Estimate of possible loss 45    
Maximum      
Estimated capital costs to comply with existing and known federal and state air emissions regulations 100    
Maximum | Ameren Missouri      
Estimated capital costs to comply with existing and known federal and state air emissions regulations 100    
Maximum | Manufactured Gas Plant | Ameren Illinois      
Estimate of possible loss 90    
New CCR Rules Estimate      
Asset Retirement Obligation 56    
New CCR Rules Estimate | Ameren Missouri      
Asset Retirement Obligation $ 56