Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Short-term Debt [Line Items]
Average daily amount outstanding	$ 578	$ 1,168
Weighted-average interest rate	5.56%	5.10%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,084	$ 1,381
Peak interest rate	5.68%	5.60%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 84	$ 595
Weighted-average interest rate	5.55%	5.14%
Short-term Debt, Maximum Amount Outstanding During Period	$ 301	$ 841
Peak interest rate	5.60%	5.55%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 109	$ 343
Weighted-average interest rate	5.53%	5.04%
Short-term Debt, Maximum Amount Outstanding During Period	$ 509	$ 592
Peak interest rate	5.68%	5.55%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 385	$ 230
Weighted-average interest rate	5.57%	5.10%
Short-term Debt, Maximum Amount Outstanding During Period	$ 694	$ 450
Peak interest rate	5.68%	5.60%