Property And Plant, Net (Accrued Capital Expenditures) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	[1]	$ 235	$ 181	$ 175
Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures		85	72	74
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures		92	59	86
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	[1]	16	13	8
Nuclear Fuel | Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures		$ 16	$ 13	$ 8

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