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Property and Plant, Net (Schedule of Capitalized Software and Deferred Cloud Implementation Costs) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Capitalized software costs      
Finite-Lived Intangible Assets [Line Items]      
Capitalized Computer Software, Amortization $ 222 $ 224 $ 212
Capitalized Computer Software, Gross 1,174 1,996  
Capitalized Computer Software, Accumulated Amortization (572) (1,348)  
Hosting Arrangement, Service Contract, Implementation Cost, Expense, Amortization 19 20 17
Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, before Accumulated Amortization 142 157  
Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, Accumulated Amortization (59) (71)  
Ameren Missouri | Capitalized software costs      
Finite-Lived Intangible Assets [Line Items]      
Capitalized Computer Software, Amortization 113 118 114
Capitalized Computer Software, Gross 562 881  
Capitalized Computer Software, Accumulated Amortization (290) (567)  
Hosting Arrangement, Service Contract, Implementation Cost, Expense, Amortization 8 9 8
Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, before Accumulated Amortization 63 71  
Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, Accumulated Amortization (28) (32)  
Ameren Illinois | Capitalized software costs      
Finite-Lived Intangible Assets [Line Items]      
Capitalized Computer Software, Amortization 101 100 92
Capitalized Computer Software, Gross 570 867  
Capitalized Computer Software, Accumulated Amortization (261) (552)  
Hosting Arrangement, Service Contract, Implementation Cost, Expense, Amortization 10 10 $ 9
Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, before Accumulated Amortization 76 82  
Hosting Arrangement, Service Contract, Implementation Cost, Capitalized, Accumulated Amortization $ (29) $ (36)  
Minimum | Software and Software Development Costs      
Finite-Lived Intangible Assets [Line Items]      
Property, Plant and Equipment, Useful Life 2 years    
Minimum | Capitalized software costs      
Finite-Lived Intangible Assets [Line Items]      
Finite-Lived Intangible Asset, Useful Life 5 years    
Maximum | Software and Software Development Costs      
Finite-Lived Intangible Assets [Line Items]      
Property, Plant and Equipment, Useful Life 15 years    
Maximum | Capitalized software costs      
Finite-Lived Intangible Assets [Line Items]      
Finite-Lived Intangible Asset, Useful Life 15 years