Short-Term Debt and Liquidity (Short-Term Debt Activity) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Short-term Debt [Line Items]
Average daily amount outstanding	$ 791	$ 665
Weighted-average interest rate	1.47%	0.22%
Short-term Debt, Maximum Amount Outstanding During Period	$ 1,222	$ 1,134
Peak interest rate	3.60%	0.33%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 439	$ 404
Weighted-average interest rate	1.58%	0.23%
Short-term Debt, Maximum Amount Outstanding During Period	$ 690	$ 650
Peak interest rate	3.55%	0.33%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 253	$ 121
Weighted-average interest rate	1.16%	0.22%
Short-term Debt, Maximum Amount Outstanding During Period	$ 539	$ 546
Peak interest rate	3.55%	0.25%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 99	$ 140
Weighted-average interest rate	1.77%	0.22%
Short-term Debt, Maximum Amount Outstanding During Period	$ 354	$ 485
Peak interest rate	3.60%	0.25%