Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Short-term Debt [Line Items]
Average daily amount outstanding	$ 1,174	$ 791
Weighted-average interest rate	5.24%	1.47%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,381	$ 1,222
Peak interest rate	5.60%	3.60%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 687	$ 439
Weighted-average interest rate	5.29%	1.58%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,127	$ 690
Peak interest rate	5.60%	3.55%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 306	$ 253
Weighted-average interest rate	5.15%	1.16%
Short-term Debt, Maximum Amount Outstanding During Period	$ 592	$ 539
Peak interest rate	5.60%	3.55%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 181	$ 99
Weighted-average interest rate	5.15%	1.77%
Short-term Debt, Maximum Amount Outstanding During Period	$ 450	$ 354
Peak interest rate	5.60%	3.60%