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Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2022
Sep. 30, 2021
Sep. 30, 2022
Sep. 30, 2021
Dec. 31, 2021
Allowance for Doubtful Accounts Receivable [Roll Forward]          
Beginning of period $ 30 $ 42 $ 29 $ 50  
Bad debt expense 15 7 26 8  
Net write-offs (14) (13) (24) (22)  
End of period 31 $ 36 31 $ 36  
Payables for purchased receivables $ 32   $ 32   $ 27
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement 17.00% 18.00% 17.00% 18.00%  
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement $ 117 $ 97 $ 117 $ 97  
Union Electric Company          
Allowance for Doubtful Accounts Receivable [Roll Forward]          
Beginning of period 12 16 13 16  
Bad debt expense 3 2 6 5  
Net write-offs (3) (4) (7) (7)  
End of period $ 12 $ 14 $ 12 $ 14  
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement 12.00% 12.00% 12.00% 12.00%  
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement $ 39 $ 33 $ 39 $ 33  
Ameren Illinois Company          
Allowance for Doubtful Accounts Receivable [Roll Forward]          
Beginning of period 18 26 16 34  
Bad debt expense 12 5 20 3  
Net write-offs (11) (9) (17) (15)  
End of period 19 $ 22 19 $ 22  
Payables for purchased receivables $ 32   $ 32   $ 27
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement 21.00% 25.00% 21.00% 25.00%  
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement $ 78 $ 64 $ 78 $ 64