Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 30	$ 30
Bad debt expense	16	10
Charged to other accounts	1	3
Net write-offs	(6)	(6)
End of period	41	37
Payables for purchased receivables	47		$ 43
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	12	12
Bad debt expense	2	1
Net write-offs	(2)	(2)
End of period	12	11
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	18	18
Bad debt expense	14	9
Charged to other accounts	1	3
Net write-offs	(4)	(4)
End of period	29	$ 26
Payables for purchased receivables	$ 47		$ 43