Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 37	$ 39	$ 30	$ 31
Bad debt expense	12	18	28	41
Charged to other accounts	2	2	6	3
Net write-offs	(20)	(26)	(33)	(42)
End of period	31	33	31	33
Payables for purchased receivables	53		53		$ 42
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	12	12	12	13
Bad debt expense	3	5	8	9
Net write-offs	(3)	(5)	(8)	(10)
End of period	12	12	12	12
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	25	27	18	18
Bad debt expense	9	13	20	32
Charged to other accounts	2	2	6	3
Net write-offs	(17)	(21)	(25)	(32)
End of period	19	$ 21	19	$ 21
Payables for purchased receivables	$ 53		$ 53		$ 42