Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) $ in Millions		Dec. 31, 2015 USD ($) equipment	Dec. 31, 2014 USD ($)
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1]	$ 27,603	$ 26,198
Accumulated depreciation and amortization	[1]	10,347	9,759
Property and plant, before construction work in progress	[1]	17,256	16,439
Property, Plant and Equipment, Net	[1]	$ 18,799	17,424
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		$ 233
Total accumulated depreciation, capital lease agreements		72	66
Held-to-maturity Securities		288	294
Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1]	25,161	23,913
Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1]	2,442	2,285
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	[1]	275	209
Other Energy
Property, Plant and Equipment [Line Items]
Construction work in progress	[1]	1,268	776
Union Electric Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1]	17,966	17,483
Accumulated depreciation and amortization	[1]	7,460	7,086
Property and plant, before construction work in progress	[1]	10,506	10,397
Property, Plant and Equipment, Net	[1]	11,183	10,867
Union Electric Company | Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1]	17,521	17,052
Union Electric Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	[1]	445	431
Union Electric Company | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	[1]	275	209
Union Electric Company | Other Energy
Property, Plant and Equipment [Line Items]
Construction work in progress	[1]	402	261
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost		9,250	8,371
Accumulated depreciation and amortization		2,632	2,422
Property and plant, before construction work in progress		6,618	5,949
Property, Plant and Equipment, Net		6,848	6,165
Ameren Illinois Company | Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost		7,253	6,517
Ameren Illinois Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost		1,997	1,854
Ameren Illinois Company | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress		0	0
Ameren Illinois Company | Other Energy
Property, Plant and Equipment [Line Items]
Construction work in progress		230	216
Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost		387	344
Accumulated depreciation and amortization		255	251
Property and plant, before construction work in progress		132	93
Property, Plant and Equipment, Net		768	392
Other | Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost		387	344
Other | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost		0	0
Other | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress		0	0
Other | Other Energy
Property, Plant and Equipment [Line Items]
Construction work in progress		$ 636	$ 299

[1] (a)Amounts in Ameren and Ameren Missouri include two CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $233 million at December 31, 2015 and 2014. The total accumulated depreciation associated with the two CTs was $72 million and $66 million at December 31, 2015 and 2014, respectively. In addition, Ameren Missouri has investments in debt securities, which were classified as held-to-maturity and recorded in "Other assets", related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2015 and 2014, the carrying value of these debt securities was $288 million and $294 million, respectively.