Income Taxes (Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Plant related	$ 3,534	$ 3,474
Regulatory assets, net	(589)	(547)
Deferred benefit costs	(126)	(131)
Revenue Requirement Reconciliation Adjustment		20
Tax carryforwards	(227)	(361)
Other	31	51
Total net accumulated deferred income tax liabilities	2,623	2,506
Union Electric Company
Income Taxes [Line Items]
Plant related	2,010	2,064
Regulatory assets, net	(343)	(317)
Deferred benefit costs	(58)	(53)
Revenue Requirement Reconciliation Adjustment		0
Tax carryforwards	(35)	(31)
Other	(40)	(13)
Total net accumulated deferred income tax liabilities	1,534	1,650
Ameren Illinois Company
Income Taxes [Line Items]
Plant related	1,345	1,264
Regulatory assets, net	(221)	(206)
Deferred benefit costs	(4)	(17)
Revenue Requirement Reconciliation Adjustment		20
Tax carryforwards	(26)	(43)
Other	25	3
Total net accumulated deferred income tax liabilities	1,119	1,021
Other
Income Taxes [Line Items]
Plant related	179	146
Regulatory assets, net	(25)	(24)
Deferred benefit costs	(64)	(61)
Revenue Requirement Reconciliation Adjustment		0
Tax carryforwards	(166)	(287)
Other	46	61
Total net accumulated deferred income tax liabilities	$ (30)	$ (165)