Long-Term Debt And Equity Financings (Narrative) (Detail) (USD $)	3 Months Ended					1 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 Ameren Missouri And Ameren Illinois [Member]	Mar. 31, 2014 Ameren Illinois Company	Mar. 31, 2014 Ameren Illinois Company Federal Energy Regulatory Commission Restriction [Member]	Mar. 31, 2014 Ameren Illinois Company Minimum Federal Energy Regulatory Commission Restriction [Member]	Jan. 31, 2014 Environmental Improvement And Pollution Control Revenue Bonds [Member] Ameren Illinois Company	Apr. 30, 2014 Subsequent Event [Member] Secured Debt [Member] Senior Secured Notes, 3.50%, Due 2024 [Member] Union Electric Company	May 31, 2014 Subsequent Event [Member] Secured Debt [Member] Senior Secured Notes550 Due2014 [Member] Union Electric Company	May 15, 2014 Subsequent Event [Member] Secured Debt [Member] Senior Secured Notes550 Due2014 [Member] Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Debt Instrument, Face Amount			$ 1,000,000				$ 350,000,000
Redemptions of Long-term Debt						163,000,000		104,000,000
Debt Instrument, Interest Rate, Stated Percentage							3.50%		5.50%
Assumed interest rate		6.00%
Dividend rate		7.00%
Excess in indebtedness upon default of maturity	25,000,000
Common stock equity to total capitalization				55.00%	30.00%
Proceeds from Issuance of Secured Debt							$ 348,000,000