Related Party Transactions (Schedule of Capital Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Union Electric Company
Related Party Transaction [Line Items]
Proceeds from Contributions from Parent	$ 45	$ 30	$ 44
Noncash Or Part Noncash Capital Contribution From Parent			38
Ameren Illinois Company
Related Party Transaction [Line Items]
Proceeds from Contributions from Parent	$ 160	$ 8	$ 0