Income Taxes (Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Net operating loss carryforwards:
Net operating loss carryforwards:	$ 65	$ 7
Tax credit carryforwards	133	90
Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	34
Tax credit carryforwards	126	83
State
Net operating loss carryforwards:
Net operating loss carryforwards:	31	7
Tax credit carryforwards	7	7
Union Electric Company
Net operating loss carryforwards:
Net operating loss carryforwards:	3	0
Tax credit carryforwards	65	26
Union Electric Company | Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	2
Tax credit carryforwards	65	26
Union Electric Company | State
Net operating loss carryforwards:
Net operating loss carryforwards:	1	0
Tax credit carryforwards	0	0
Ameren Illinois Company
Net operating loss carryforwards:
Net operating loss carryforwards:	42	3
Tax credit carryforwards	4	3
Ameren Illinois Company | Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	17
Tax credit carryforwards	3	3
Ameren Illinois Company | State
Net operating loss carryforwards:
Net operating loss carryforwards:	25	3
Tax credit carryforwards	1	0
Other
Net operating loss carryforwards:
Net operating loss carryforwards:	20	4
Tax credit carryforwards	64	61
Other | Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	15
Tax credit carryforwards	58	54
Other | State
Net operating loss carryforwards:
Net operating loss carryforwards:	5	4
Tax credit carryforwards	$ 6	$ 7