Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 45	$ 39	$ 39	$ 30
Bad debt expense	21	18	42	37
Charged to other accounts	3	2	6	5
Net write-offs	(22)	(21)	(40)	(34)
End of period	47	38	47	38
Payables for purchased receivables	65		65		$ 47
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	17	12	17	12
Bad debt expense	7	7	13	11
Net write-offs	(5)	(4)	(11)	(8)
End of period	19	15	19	15
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	28	27	22	18
Bad debt expense	14	11	29	26
Charged to other accounts	3	2	6	5
Net write-offs	(17)	(17)	(29)	(26)
End of period	28	$ 23	28	$ 23
Payables for purchased receivables	$ 65		$ 65		$ 47