Property And Plant, Net (Accrued Capital Expenditures) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	$ 175	[1]	$ 107	[1]	$ 97	[1]
Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	74		63		73
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	86		37		18
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	8	[1]	8	[1]	36	[1]
Nuclear Fuel | Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	$ 8		$ 8		$ 36

[1] Includes amounts for Ameren registrant and nonregistrant subsidiaries.