Supplemental Information (Schedule of Excise Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Line Items]
Excise Tax Expense	$ 275	$ 254	$ 264
Union Electric Company
Accounting Policies [Line Items]
Excise Tax Expense	150	139	147
Ameren Illinois Company
Accounting Policies [Line Items]
Excise Tax Expense	$ 125	$ 115	$ 117