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Short-Term Debt And Liquidity (Commercial Paper) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Short-term Debt [Line Items]
Average daily amount outstanding	$ 940	$ 762
Commercial paper issuances outstanding at period-end	$ 643	$ 1,143
Weighted-average interest rate	4.49%	5.28%
Peak amount outstanding during period	$ 1,603	$ 1,569
Peak interest rate	4.75%	5.68%
Ameren (parent)
Short-term Debt [Line Items]
Average daily amount outstanding	$ 620	$ 377
Commercial paper issuances outstanding at period-end	$ 155	$ 1,055
Weighted-average interest rate	4.48%	5.10%
Peak amount outstanding during period	$ 1,139	$ 1,091
Peak interest rate	4.75%	5.60%
Ameren Missouri
Short-term Debt [Line Items]
Average daily amount outstanding	$ 223	$ 192
Commercial paper issuances outstanding at period-end	$ 471	$ 0
Weighted-average interest rate	4.48%	5.34%
Peak amount outstanding during period	$ 650	$ 595
Peak interest rate	4.72%	5.68%
Ameren Illinois
Short-term Debt [Line Items]
Average daily amount outstanding	$ 97	$ 193
Commercial paper issuances outstanding at period-end	$ 17	$ 88
Weighted-average interest rate	4.55%	5.57%
Peak amount outstanding during period	$ 425	$ 694
Peak interest rate	4.70%	5.68%

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