Supplemental Information (Schedule of Excise Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Line Items]
Excise Tax Expense	$ 264	$ 282	$ 265
Union Electric Company
Accounting Policies [Line Items]
Excise Tax Expense	147	164	153
Ameren Illinois Company
Accounting Policies [Line Items]
Excise Tax Expense	$ 117	$ 118	$ 112