Short-Term Debt And Liquidity (Schedule Of Maximum Aggregate Amount Available On Credit Agreements) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 2,300
Missouri Credit Agreement 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,200	$ 1,000
Missouri Credit Agreement 2012 | Parent Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	900
Missouri Credit Agreement 2012 | Union Electric Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	850
Illinois Credit Agreement 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,100
Illinois Credit Agreement 2012 | Parent Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	500
Illinois Credit Agreement 2012 | Ameren Illinois Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 800