Long-Term Debt And Equity Financings (Narrative) (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($)
Ameren Missouri And Ameren Illinois
Long-Term Debt And Equity Financings [Line Items]
Assumed interest rate	5.00%
Dividend rate	6.00%
Secured Debt | Senior Secured Notes540 Due2016 [Member] | Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount	$ 260,000,000
Debt Instrument, Interest Rate, Stated Percentage	5.40%
Federal Energy Regulatory Commission Restriction [Member] | Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Common stock equity to total capitalization	51.00%
Federal Energy Regulatory Commission Restriction [Member] | Ameren Illinois Company | Minimum
Long-Term Debt And Equity Financings [Line Items]
Common stock equity to total capitalization	30.00%