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Schedule II - Valuation And Qualifying Accounts (Details) - Allowance For Doubtful Accounts - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period $ 30 $ 30 $ 31
Charged to Costs and Expenses 51 39 51
Charged to Other Accounts 7 8 5
Deductions 49 47 57
Balance at End of Period 39 30 30
Ameren Missouri      
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period 12 12 13
Charged to Costs and Expenses 17 11 11
Charged to Other Accounts 0 0 0
Deductions 12 11 12
Balance at End of Period 17 12 12
Ameren Illinois      
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period 18 18 18
Charged to Costs and Expenses 34 28 40
Charged to Other Accounts 7 8 5
Deductions 37 36 45
Balance at End of Period $ 22 $ 18 $ 18