Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	$ 31	$ 29
Bad debt expense	10	4
Net write-offs	(7)	(5)
End of period	34	$ 28
Payables for purchased receivables	$ 35		$ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	23.00%	20.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 153	$ 116
Union Electric Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	13	13
Bad debt expense	2	1
Net write-offs	(3)	(3)
End of period	$ 12	$ 11
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	15.00%	15.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 33	$ 31
Ameren Illinois Company
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning of period	18	16
Bad debt expense	8	3
Net write-offs	(4)	(2)
End of period	22	$ 17
Payables for purchased receivables	$ 35		$ 31
Percentage of accounts receivable balances that are 30 days past due or are part of a deferred payment arrangement	28.00%	23.00%
Accounts receivable balances that are 30 days or more past due or part of a deferred payment arrangement	$ 120	$ 85