Short-Term Debt And Liquidity (Commercial Paper) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Short-term Debt [Line Items]
Average daily amount outstanding	$ 1,166	$ 852
Commercial paper issuances outstanding at period-end	$ 536	$ 1,070
Weighted-average interest rate	5.32%	2.28%
Peak amount outstanding during period	$ 1,526	$ 1,267
Peak interest rate	5.68%	4.95%
Ameren (parent)
Short-term Debt [Line Items]
Average daily amount outstanding	$ 726	$ 485
Commercial paper issuances outstanding at period-end	$ 0	$ 477
Weighted-average interest rate	5.38%	2.41%
Peak amount outstanding during period	$ 1,298	$ 718
Peak interest rate	5.65%	4.80%
Ameren Missouri
Short-term Debt [Line Items]
Average daily amount outstanding	$ 274	$ 229
Commercial paper issuances outstanding at period-end	$ 170	$ 329
Weighted-average interest rate	5.22%	1.71%
Peak amount outstanding during period	$ 592	$ 539
Peak interest rate	5.68%	4.95%
Ameren Illinois
Short-term Debt [Line Items]
Average daily amount outstanding	$ 166	$ 138
Commercial paper issuances outstanding at period-end	$ 366	$ 264
Weighted-average interest rate	5.23%	2.79%
Peak amount outstanding during period	$ 450	$ 404
Peak interest rate	5.68%	4.80%