Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 39	$ 30	$ 31	$ 29
Bad debt expense	18	14	41	23
Charged to other accounts	2	1	3	3
Net write-offs	(26)	(14)	(42)	(24)
End of period	33	$ 31	33	$ 31
Payables for purchased receivables	$ 50		$ 50		$ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	17.00%	17.00%	17.00%	17.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 106	$ 117	$ 106	$ 117
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	12	12	13	13
Bad debt expense	5	3	9	6
Net write-offs	(5)	(3)	(10)	(7)
End of period	$ 12	$ 12	$ 12	$ 12
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	8.00%	12.00%	8.00%	12.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 25	$ 39	$ 25	$ 39
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	27	18	18	16
Bad debt expense	13	11	32	17
Charged to other accounts	2	1	3	3
Net write-offs	(21)	(11)	(32)	(17)
End of period	21	$ 19	21	$ 19
Payables for purchased receivables	$ 50		$ 50		$ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	26.00%	21.00%	26.00%	21.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 81	$ 78	$ 81	$ 78