Retirement Benefits (Cash Contributions Made To Benefit Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	$ 4	$ 5	$ 60
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	3	2	2
Ameren Missouri | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	1	1	22
Ameren Missouri | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	2	1	1
Ameren Illinois | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	2	3	28
Ameren Illinois | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	1	1	1
Other | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	1	1	10
Other | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	$ 0	$ 0	$ 0