Consolidated Statement Of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Paid, Capitalized	$ 14	$ 15	$ 17
Union Electric Company
Interest Paid, Capitalized	10	12	12
Ameren Illinois Company
Interest Paid, Capitalized	$ 4	$ 3	$ 5