Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Short-term Debt [Line Items]
Average daily amount outstanding	$ 1,175	$ 789
Weighted-average interest rate	4.88%	0.41%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,381	$ 1,101
Peak interest rate	5.60%	1.15%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 506	$ 282
Weighted-average interest rate	4.89%	0.41%
Short-term Debt, Maximum Amount Outstanding During Period	$ 728	$ 466
Peak interest rate	5.55%	1.05%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 436	$ 408
Weighted-average interest rate	4.86%	0.44%
Short-term Debt, Maximum Amount Outstanding During Period	$ 592	$ 539
Peak interest rate	5.55%	1.06%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 233	$ 99
Weighted-average interest rate	4.89%	0.33%
Short-term Debt, Maximum Amount Outstanding During Period	$ 325	$ 142
Peak interest rate	5.60%	1.15%