Long-Term Debt And Equity Financings (Schedule Of Covered Ratio) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Bonds Issuable	$ 4,018	[1]
Preferred Stock Issuable	2,272
Retired bond capacity	729
Union Electric Company | Actual Ratio [Member]
Long-Term Debt And Equity Financings [Line Items]
Restricted payment interest coverage ratio, Actual	4.7
Dividend Coverage Ratio	118.8
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Bonds Issuable	3,732	[1],[2]
Preferred Stock Issuable	203	[3]
Retired bond capacity	$ 454
Ameren Illinois Company | Actual Ratio [Member]
Long-Term Debt And Equity Financings [Line Items]
Restricted payment interest coverage ratio, Actual	7.6
Dividend Coverage Ratio	2.7
Minimum | Union Electric Company | Minimum Required Ratio [Member]
Long-Term Debt And Equity Financings [Line Items]
Restricted payment interest coverage ratio, Actual	2.0	[4]
Dividend Coverage Ratio	2.5	[5]
Minimum | Ameren Illinois Company | Minimum Required Ratio [Member]
Long-Term Debt And Equity Financings [Line Items]
Restricted payment interest coverage ratio, Actual	2.0	[4]
Dividend Coverage Ratio	1.5	[5]

[1] Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $729 million and $454 million at Ameren Missouri and Ameren Illinois, respectively.

[2] Amount of bonds issuable by Ameren Illinois based on unfunded property additions and retired bonds solely under the former IP mortgage indenture.

[3] Preferred stock issuable is restricted by the amount of preferred stock that is currently authorized by Ameren Illinois’ articles of incorporation.

[4] Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds.

[5] Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation.