Property And Plant, Net (Accrued Capital Expenditures) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	[1]	$ 251	$ 235	$ 181
Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures		116	85	72
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures		87	92	59
Nuclear Fuel
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	[1]	20	16	13
Nuclear Fuel | Union Electric Company
Property, Plant and Equipment [Line Items]
Accrued capital expenditures		$ 20	$ 16	$ 13

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