Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) equipment	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	$ 34,002	$ 32,027
Accumulated depreciation and amortization	12,273	11,633
Property and plant, before construction work in progress	21,729	20,394
Property, Plant and Equipment, Net	$ 22,810	21,466
Number of combustion turbine electric generation equipment under capital lease agreements | equipment	2
Number of capital lease agreements | equipment	2
Capital lease agreements, gross asset value	$ 235	233
Total accumulated depreciation, capital lease agreements	89	83
Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	11,432	11,132
Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	11,959	11,415
Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,309	4,666
Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,201	2,893
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	2,101	1,921
Construction work in progress	864	924
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	217	148
Union Electric Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	20,206	19,495
Accumulated depreciation and amortization	8,726	8,305
Property and plant, before construction work in progress	11,480	11,190
Property, Plant and Equipment, Net	12,103	11,751
Union Electric Company | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	11,432	11,132
Union Electric Company | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,989	5,766
Union Electric Company | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,277	1,201
Union Electric Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	500	474
Union Electric Company | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,008	922
Construction work in progress	406	413
Union Electric Company | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	217	148
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	12,181	11,123
Accumulated depreciation and amortization	3,294	3,082
Property and plant, before construction work in progress	8,887	8,041
Property, Plant and Equipment, Net	9,198	8,293
Ameren Illinois Company | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,970	5,649
Ameren Illinois Company | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	2,647	2,298
Ameren Illinois Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	2,701	2,419
Ameren Illinois Company | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	863	757
Construction work in progress	311	252
Ameren Illinois Company | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	0	0
Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,615	1,409
Accumulated depreciation and amortization	253	246
Property and plant, before construction work in progress	1,362	1,163
Property, Plant and Equipment, Net	1,509	1,422
Other | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,385	1,167
Other | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	230	242
Construction work in progress	147	259
Other | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 0	$ 0
Minimum | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Minimum | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Minimum | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Minimum | Gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Minimum | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Maximum | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	72 years
Maximum | Electric distribution equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	80 years
Maximum | Electric transmission equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	75 years
Maximum | Gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	80 years
Maximum | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	55 years
Maximum | Union Electric Company | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	150 years