Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Short-term Debt [Line Items]
Average daily amount outstanding	$ 471	$ 1,175
Weighted-average interest rate	5.57%	4.88%
Short-term Debt, Maximum Amount Outstanding During Period	$ 869	$ 1,381
Peak interest rate	5.68%	5.60%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 0	$ 506
Weighted-average interest rate	0.00%	4.89%
Short-term Debt, Maximum Amount Outstanding During Period	$ 0	$ 728
Peak interest rate	0.00%	5.55%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 135	$ 436
Weighted-average interest rate	5.53%	4.86%
Short-term Debt, Maximum Amount Outstanding During Period	$ 444	$ 592
Peak interest rate	5.68%	5.55%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 336	$ 233
Weighted-average interest rate	5.58%	4.89%
Short-term Debt, Maximum Amount Outstanding During Period	$ 425	$ 325
Peak interest rate	5.68%	5.60%