Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Property and plant, at original cost	$ 26,468	[1],[2]	$ 26,154	[1],[2]
Accumulated depreciation and amortization	9,429	[1],[2]	9,194	[1],[2]
Property and plant, before construction work in progress	17,039	[1],[2]	16,960	[1],[2]
Property and Plant, Net	18,127	[1],[2]	17,853	[1],[2]
Capital lease agreements, gross asset value	229		228
Total accumulated depreciation, capital lease agreements	52		46
Electric [Member]
Property and plant, at original cost	24,256	[1],[2]	24,069	[1],[2]
Gas [Member]
Property and plant, at original cost	1,746	[1],[2]	1,661	[1],[2]
Other Energy [Member]
Property and plant, at original cost	466	[1],[2]	424	[1],[2]
Construction work in progress	833	[1],[2]	634	[1],[2]
Nuclear Fuel [Member]
Construction work in progress	$ 255	[1],[2]	$ 259	[1],[2]

[1] Includes amounts for Ameren registrant and nonregistrant subsidiaries as well as intercompany eliminations.

[2] Amounts in Ameren and Ameren Missouri include two electric generation CTs under two separate capital lease agreements. The gross asset value of those agreements was $229 million and $228 million at December 31, 2011 and 2010, respectively. The total accumulated depreciation associated with the two CTs was $52 million and $46 million at December 31, 2011 and 2010, respectively.