Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Short-term Debt [Line Items]
Average daily amount outstanding	$ 620	$ 1,174
Weighted-average interest rate	5.53%	5.24%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,542	$ 1,381
Peak interest rate	5.68%	5.60%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 177	$ 687
Weighted-average interest rate	5.46%	5.29%
Short-term Debt, Maximum Amount Outstanding During Period	$ 948	$ 1,127
Peak interest rate	5.60%	5.60%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 187	$ 306
Weighted-average interest rate	5.52%	5.15%
Short-term Debt, Maximum Amount Outstanding During Period	$ 576	$ 592
Peak interest rate	5.68%	5.60%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 256	$ 181
Weighted-average interest rate	5.57%	5.15%
Short-term Debt, Maximum Amount Outstanding During Period	$ 694	$ 450
Peak interest rate	5.68%	5.60%