Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Short-term Debt [Line Items]
Average daily amount outstanding	$ 1,293	$ 471
Weighted-average interest rate	4.60%	5.57%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,603	$ 869
Peak interest rate	4.75%	5.68%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 898	$ 0
Weighted-average interest rate	4.61%	0.00%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,139	$ 0
Peak interest rate	4.75%	0.00%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 313	$ 135
Weighted-average interest rate	4.59%	5.53%
Short-term Debt, Maximum Amount Outstanding During Period	$ 630	$ 444
Peak interest rate	4.70%	5.68%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 82	$ 336
Weighted-average interest rate	4.56%	5.58%
Short-term Debt, Maximum Amount Outstanding During Period	$ 189	$ 425
Peak interest rate	4.69%	5.68%