Short-Term Debt And Liquidity (Commercial Paper) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Average daily amount outstanding	$ 604	$ 263
Commercial paper issuances outstanding at period-end	$ 545	$ 490
Weighted-average interest rate	0.22%	1.31%
Peak amount outstanding during period(a)	$ 1,134	$ 908
Peak interest rate	0.38%	5.05%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 387	$ 108
Commercial paper issuances outstanding at period-end	$ 277	$ 490
Weighted-average interest rate	0.22%	1.04%
Peak amount outstanding during period(a)	$ 650	$ 490
Peak interest rate	0.38%	3.30%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 99	$ 109
Commercial paper issuances outstanding at period-end	$ 165	$ 0
Weighted-average interest rate	0.22%	1.73%
Peak amount outstanding during period(a)	$ 546	$ 573
Peak interest rate	0.35%	5.05%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 118	$ 46
Commercial paper issuances outstanding at period-end	$ 103	$ 0
Weighted-average interest rate	0.21%	0.97%
Peak amount outstanding during period(a)	$ 485	$ 250
Peak interest rate	0.35%	3.40%