Short-Term Debt And Liquidity (Commercial Paper) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Short-term Debt [Line Items]
Average daily amount outstanding	$ 762	$ 1,166
Commercial paper issuances outstanding at period-end	$ 1,143	$ 536
Weighted-average interest rate	5.28%	5.32%
Peak amount outstanding during period	$ 1,569	$ 1,526
Peak interest rate	5.68%	5.68%
Ameren (parent)
Short-term Debt [Line Items]
Average daily amount outstanding	$ 377	$ 726
Commercial paper issuances outstanding at period-end	$ 1,055	$ 0
Weighted-average interest rate	5.10%	5.38%
Peak amount outstanding during period	$ 1,091	$ 1,298
Peak interest rate	5.60%	5.65%
Ameren Missouri
Short-term Debt [Line Items]
Average daily amount outstanding	$ 192	$ 274
Commercial paper issuances outstanding at period-end	$ 0	$ 170
Weighted-average interest rate	5.34%	5.22%
Peak amount outstanding during period	$ 595	$ 592
Peak interest rate	5.68%	5.68%
Ameren Illinois
Short-term Debt [Line Items]
Average daily amount outstanding	$ 193	$ 166
Commercial paper issuances outstanding at period-end	$ 88	$ 366
Weighted-average interest rate	5.57%	5.23%
Peak amount outstanding during period	$ 694	$ 450
Peak interest rate	5.68%	5.68%