Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 37	$ 34	$ 30	$ 31
Bad debt expense	6	13	16	23
Charged to other accounts	1	1	4	1
Net write-offs	(7)	(9)	(13)	(16)
End of period	37	39	37	39
Payables for purchased receivables	49		49		$ 42
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	11	12	12	13
Bad debt expense	4	2	5	4
Net write-offs	(3)	(2)	(5)	(5)
End of period	12	12	12	12
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	26	22	18	18
Bad debt expense	2	11	11	19
Charged to other accounts	1	1	4	1
Net write-offs	(4)	(7)	(8)	(11)
End of period	25	$ 27	25	$ 27
Payables for purchased receivables	$ 49		$ 49		$ 42