Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) equipment	Dec. 31, 2019 USD ($)
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	$ 39,719	$ 36,652
Accumulated depreciation and amortization	13,773	13,006
Property and plant, before construction work in progress	25,946	23,646
Property, Plant and Equipment, Net	$ 26,807	24,376
Number of combustion turbine electric generation equipment with related financing obligations | equipment	2
Number of financing obligations | equipment	2
Gross asset value, financing obligations	$ 240	236
Total accumulated depreciation, financing obligations	99	95
Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	4,875	4,730
Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,097	1,090
Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,608	5,414
Renewable Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,301	646
Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	13,433	12,670
Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	6,831	6,148
Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,869	3,552
Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	2,705	2,402
Construction work in progress	786	595
Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	75	135
Oil Fired Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost		36
Union Electric Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	23,098	21,357
Accumulated depreciation and amortization	9,689	9,195
Property and plant, before construction work in progress	13,409	12,162
Property, Plant and Equipment, Net	13,879	12,635
Union Electric Company | Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	4,875	4,730
Union Electric Company | Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,097	1,090
Union Electric Company | Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,608	5,414
Union Electric Company | Renewable Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,301	646
Union Electric Company | Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	6,784	6,371
Union Electric Company | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,482	1,405
Union Electric Company | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	561	528
Union Electric Company | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,390	1,173
Construction work in progress	395	338
Union Electric Company | Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	75	135
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	14,602	13,417
Accumulated depreciation and amortization	3,780	3,536
Property and plant, before construction work in progress	10,822	9,881
Property, Plant and Equipment, Net	11,201	10,083
Ameren Illinois Company | Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Renewable Electric Generation Equipment
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	6,649	6,299
Ameren Illinois Company | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,575	3,101
Ameren Illinois Company | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,308	3,024
Ameren Illinois Company | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,070	993
Construction work in progress	379	202
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	2,019	1,878
Accumulated depreciation and amortization	304	275
Property and plant, before construction work in progress	1,715	1,603
Property, Plant and Equipment, Net	1,727	1,658
Other | Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Renewable Electric Generation Equipment
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	1,774	1,642
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	245	236
Construction work in progress	12	55
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