Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ (84)	$ (148)	$ (4)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(79)	(83)	(54)
Ameren Missouri | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(44)	(76)	(3)
Ameren Missouri | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(27)	(30)	(14)
Ameren Illinois | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(34)	(62)	3
Ameren Illinois | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(52)	(54)	(41)
Other | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(6)	(10)	(4)
Other | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 0	$ 1	$ 1