Schedule II - Valuation And Qualifying Accounts (Details) - Allowance For Doubtful Accounts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 50	$ 17	$ 18
Charged to Costs and Expenses	9	42	26
Charged to Other Accounts	0	6	4
Deductions	30	15	31
Balance at End of Period	29	50	17
Union Electric Company
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	16	7	7
Charged to Costs and Expenses	5	15	9
Charged to Other Accounts	0	0	0
Deductions	8	6	9
Balance at End of Period	13	16	7
Ameren Illinois Company
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	34	10	11
Charged to Costs and Expenses	4	27	17
Charged to Other Accounts	0	6	4
Deductions	22	9	22
Balance at End of Period	$ 16	$ 34	$ 10