Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 28	$ 47	$ 29	$ 50
Bad debt expense	7	(3)	11	1
Net write-offs	(5)	(2)	(10)	(9)
End of period	30	42	30	42
Payables for purchased receivables	32		32		$ 27
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	11	15	13	16
Bad debt expense	2	2	3	3
Net write-offs	(1)	(1)	(4)	(3)
End of period	12	16	12	16
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	17	32	16	34
Bad debt expense	5	(5)	8	(2)
Net write-offs	(4)	(1)	(6)	(6)
End of period	18	$ 26	18	$ 26
Payables for purchased receivables	$ 32		$ 32		$ 27