Short-Term Debt And Liquidity (Schedule Of Maximum Aggregate Amount Available On Credit Agreements) (Details)	Dec. 31, 2018 USD ($)
Illinois Credit Agreement 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,300,000,000.0
Illinois Credit Agreement 2012 | Parent Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	500,000,000
Illinois Credit Agreement 2012 | Ameren Illinois Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	800,000,000
Missouri Credit Agreement 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,200,000,000.0
Missouri Credit Agreement 2012 | Parent Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	700,000,000
Missouri Credit Agreement 2012 | Union Electric Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 800,000,000