Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 30	$ 31
Bad debt expense	10	10
Charged to other accounts	3	0
Net write-offs	(6)	(7)
End of period	37	34
Payables for purchased receivables	43		$ 42
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	12	13
Bad debt expense	1	2
Net write-offs	(2)	(3)
End of period	11	12
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	18	18
Bad debt expense	9	8
Charged to other accounts	3	0
Net write-offs	(4)	(4)
End of period	26	$ 22
Payables for purchased receivables	$ 43		$ 42