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Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Related Party Transaction [Line Items]    
Accounts receivable - affiliates $ 665 $ 525
Ameren Missouri | Related Party    
Related Party Transaction [Line Items]    
Accounts receivable - affiliates 15 40
Ameren Missouri | Income taxes payable to parent | Related Party    
Related Party Transaction [Line Items]    
Income taxes payable to parent 0 0
Ameren Missouri | Income taxes receivable from parent | Related Party    
Related Party Transaction [Line Items]    
Accounts receivable - affiliates 3 28
Ameren Illinois | Related Party    
Related Party Transaction [Line Items]    
Accounts receivable - affiliates 18 15
Ameren Illinois | Income taxes payable to parent | Related Party    
Related Party Transaction [Line Items]    
Income taxes payable to parent 4 32
Ameren Illinois | Income taxes receivable from parent | Related Party    
Related Party Transaction [Line Items]    
Accounts receivable - affiliates $ 7 $ 0