Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013 equipment		Dec. 31, 2012 agreement equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	$ 23,701	[1],[2]	$ 22,796	[1],[2]
Accumulated depreciation and amortization	8,644	[1],[2]	8,346	[1],[2]
Property and plant, before construction work in progress	15,057	[1],[2]	14,450	[1],[2]
Property, Plant and Equipment, Net	16,205	[1],[2]	15,348	[1],[2]
Number of combustion turbine electric generation equipment under capital lease agreements	2		2
Number of capital lease agreements	2		2
Capital lease agreements, gross asset value	228		228
Total accumulated depreciation, capital lease agreements	56		52
Held-to-maturity Securities	299		304
Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	21,726	[1],[2]	20,942	[1],[2]
Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,975	[1],[2]	1,854	[1],[2]
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	246	[1],[2]	317	[1],[2]
Other Energy
Property, Plant and Equipment [Line Items]
Construction work in progress	902	[1],[2]	581	[1],[2]
Union Electric Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	16,377	[1]	16,031	[1]
Accumulated depreciation and amortization	6,766	[1]	6,614	[1]
Property and plant, before construction work in progress	9,611	[1]	9,417	[1]
Property, Plant and Equipment, Net	10,452	[1]	10,161	[1]
Union Electric Company | Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	15,964	[1]	15,638	[1]
Union Electric Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	413	[1]	393	[1]
Union Electric Company | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	246	[1]	317	[1]
Union Electric Company | Other Energy
Property, Plant and Equipment [Line Items]
Construction work in progress	595	[1]	427	[1]
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	6,988		6,446
Accumulated depreciation and amortization	1,627		1,495
Property and plant, before construction work in progress	5,361		4,951
Property, Plant and Equipment, Net	5,589		5,052
Ameren Illinois Company | Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,426		4,985
Ameren Illinois Company | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,562		1,461
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	228		101
Other Affiliates [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	336		319
Accumulated depreciation and amortization	251		237
Property and plant, before construction work in progress	85		82
Property, Plant and Equipment, Net	164		135
Other Affiliates [Member] | Electric
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	336		319
Other Affiliates [Member] | Gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0		0
Other Affiliates [Member] | Nuclear Fuel
Property, Plant and Equipment [Line Items]
Construction work in progress	0		0
Other Affiliates [Member] | Other Energy
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 79		$ 53

[1] (a)Amounts in Ameren and Ameren Missouri include two electric generation CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $228 million at December 31, 2013, and $228 million at December 31, 2012. The total accumulated depreciation associated with the two CTs was $56 million and $52 million at December 31, 2013, and 2012, respectively. In addition, Ameren Missouri has investments in debt securities, which were classified as held-to-maturity, related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2013, and 2012, the carrying value of these debt securities was $299 million and $304 million, respectively.

[2] (b)Includes amounts for Ameren registrant and nonregistrant subsidiaries.