Long-Term Debt and Equity Financings (Schedule of Required and Actual Debt Ratios) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Union Electric Company
Debt Instrument [Line Items]
Bonds Issuable Based On Coverage Ratio	$ 4,688
Preferred Stock Issuable Based On Coverage Ratio	3,153
Retired Bond Capacity	$ 2,006
Union Electric Company | Actual Interest Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	5.5
Dividend Coverage Ratio	140.8
Ameren Illinois Company
Debt Instrument [Line Items]
Bonds Issuable Based On Coverage Ratio	$ 4,234
Preferred Stock Issuable Based On Coverage Ratio	203
Retired Bond Capacity	$ 985
Ameren Illinois Company | Actual Interest Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	6.9
Dividend Coverage Ratio	3.2
Minimum | Union Electric Company | Required Dividend Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	2.0
Dividend Coverage Ratio	2.5
Minimum | Ameren Illinois Company | Required Dividend Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	2.0
Dividend Coverage Ratio	1.5