Retirement Benefits (Schedule Of Matching Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 38	$ 38	$ 35
Union Electric Company
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	21	20	19
Ameren Illinois Company
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	16	17	16
Other
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 1	$ 1	$ 0