Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) equipment	Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	$ 36,652	$ 34,002
Accumulated depreciation and amortization	13,006	12,273
Property and plant, before construction work in progress	23,646	21,729
Property, Plant and Equipment, Net	$ 24,376	22,810
Number of combustion turbine electric generation equipment with related financing obligations | equipment	2
Number of financing obligations | equipment	2
Gross asset value, financing obligations	$ 236	235
Total accumulated depreciation, financing obligations	95	89
Electric generation
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	11,880	11,432
Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	12,670	11,959
Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	6,148	5,309
Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,552	3,201
Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	2,402	2,101
Construction work in progress	595	864
Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	135	217
Union Electric Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	21,357	20,206
Accumulated depreciation and amortization	9,195	8,726
Property and plant, before construction work in progress	12,162	11,480
Property, Plant and Equipment, Net	12,635	12,103
Union Electric Company | Electric generation
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	11,880	11,432
Union Electric Company | Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	6,371	5,989
Union Electric Company | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,405	1,277
Union Electric Company | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	528	500
Union Electric Company | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,173	1,008
Construction work in progress	338	406
Union Electric Company | Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	135	217
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	13,417	12,181
Accumulated depreciation and amortization	3,536	3,294
Property and plant, before construction work in progress	9,881	8,887
Property, Plant and Equipment, Net	10,083	9,198
Ameren Illinois Company | Electric generation
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	6,299	5,970
Ameren Illinois Company | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,101	2,647
Ameren Illinois Company | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,024	2,701
Ameren Illinois Company | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	993	863
Construction work in progress	202	311
Ameren Illinois Company | Nuclear fuel in process
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	1,878	1,615
Accumulated depreciation and amortization	275	253
Property and plant, before construction work in progress	1,603	1,362
Property, Plant and Equipment, Net	1,658	1,509
Other | Electric generation
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,642	1,385
Other | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	236	230
Construction work in progress	55	147
Other | Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 0	$ 0
Minimum | Electric generation
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Minimum | Electric distribution
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Minimum | Electric transmission
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Minimum | Natural gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Minimum | Other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Maximum | Electric generation
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	72 years
Maximum | Electric distribution
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	80 years
Maximum | Electric transmission
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	75 years
Maximum | Natural gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	80 years
Maximum | Other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	55 years
Maximum | Union Electric Company | Electric generation
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	150 years