Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 41	$ 41	$ 39	$ 30
Bad debt expense	11	3	21	19
Charged to other accounts	2	2	3	3
Net write-offs	(9)	(7)	(18)	(13)
End of period	45	39	45	39
Payables for purchased receivables	46		46		$ 47
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	15	12	17	12
Bad debt expense	4	2	6	4
Net write-offs	(2)	(2)	(6)	(4)
End of period	17	12	17	12
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	26	29	22	18
Bad debt expense	7	1	15	15
Charged to other accounts	2	2	3	3
Net write-offs	(7)	(5)	(12)	(9)
End of period	28	$ 27	28	$ 27
Payables for purchased receivables	$ 46		$ 46		$ 47