Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Short-term Debt [Line Items]
Average daily amount outstanding	$ 1,168	$ 702
Weighted-average interest rate	5.10%	0.75%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,381	$ 1,101
Peak interest rate	5.60%	2.05%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 595	$ 374
Weighted-average interest rate	5.14%	0.87%
Short-term Debt, Maximum Amount Outstanding During Period	$ 841	$ 595
Peak interest rate	5.55%	2.05%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 343	$ 271
Weighted-average interest rate	5.04%	0.65%
Short-term Debt, Maximum Amount Outstanding During Period	$ 592	$ 539
Peak interest rate	5.55%	2.05%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 230	$ 57
Weighted-average interest rate	5.10%	0.47%
Short-term Debt, Maximum Amount Outstanding During Period	$ 450	$ 142
Peak interest rate	5.60%	2.05%