Property And Plant, Net (Accrued Capital Expenditures) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	$ 272	$ 361	$ 251
Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	121	159	116
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	138	175	87
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	20	10	20
Nuclear Fuel | Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	20	10	20
Nuclear Fuel | Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	$ 0	$ 0	$ 0