Retirement Benefits (Schedule Of Matching Contributions) (Details) - United States Postretirement Benefit Plan of US Entity - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 33	$ 30	$ 29
Union Electric Company
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	17	16	16
Ameren Illinois Company
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	15	13	12
Other
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 1	$ 1	$ 1