Rate And Regulatory Matters (Narrative-Missouri) (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) mi	Dec. 31, 2015 USD ($) MWh
Electric Distribution | Union Electric Company | MEEIA
Rate And Regulatory Matters [Line Items]
Incentive Award if Energy Efficiency Goals Are Achieved	$ 19,000,000
Achieved Percentage of Energy Efficiency Earnings For Incentive Award	100.00%
Incentive Award if Energy Efficiency Goals Are Achieved, Period of Recognition	3 years
Mark Twain Project | Ameren Transmission Company of Illinois
Rate And Regulatory Matters [Line Items]
Transmission Line Miles | mi	95
Noranda [Member] | Union Electric Company
Rate And Regulatory Matters [Line Items]
Revenue Requirement		$ 78,000,000
Noranda Annual Megawatthours | MWh		4,200,000.0
Noranda Operating Capacity		100.00%
Noranda Summer Base Rate		$ 45.78
Noranda Winter Base Rate		$ 31.11
Number of Months to complete MoPSC Electric Service Proceeding	11 months