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Income Taxes (Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Net operating loss carryforwards:    
Net operating loss carryforwards: $ 165 $ 93
Tax credit carryforwards: 178 410
Federal    
Net operating loss carryforwards:    
Net operating loss carryforwards: 77 30
Tax credit carryforwards: 176 408
State    
Net operating loss carryforwards:    
Net operating loss carryforwards: 88 63
Tax credit carryforwards: 2 2
Ameren Missouri    
Net operating loss carryforwards:    
Net operating loss carryforwards: 62 0
Tax credit carryforwards: 128 355
Ameren Missouri | Federal    
Net operating loss carryforwards:    
Net operating loss carryforwards: 53 0
Tax credit carryforwards: 128 355
Ameren Missouri | State    
Net operating loss carryforwards:    
Net operating loss carryforwards: 9 0
Tax credit carryforwards: 0 0
Ameren Illinois    
Net operating loss carryforwards:    
Net operating loss carryforwards: 34 34
Tax credit carryforwards: 11 11
Ameren Illinois | Federal    
Net operating loss carryforwards:    
Net operating loss carryforwards: 0 0
Tax credit carryforwards: 9 9
Ameren Illinois | State    
Net operating loss carryforwards:    
Net operating loss carryforwards: 34 34
Tax credit carryforwards: 2 2
Other    
Net operating loss carryforwards:    
Net operating loss carryforwards: 69 59
Tax credit carryforwards: 39 44
Other | Federal    
Net operating loss carryforwards:    
Net operating loss carryforwards: 24 30
Tax credit carryforwards: 39 44
Other | State    
Net operating loss carryforwards:    
Net operating loss carryforwards: 45 29
Tax credit carryforwards: $ 0 $ 0