Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ (148)	$ (4)	$ 62
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(83)	(54)	(34)
Ameren Missouri | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(76)	(3)	29
Ameren Missouri | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(30)	(14)	(4)
Ameren Illinois | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(62)	3	34
Ameren Illinois | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(54)	(41)	(31)
Other | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(10)	(4)	(1)
Other | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 1	$ 1	$ 1