Rate And Regulatory Matters Rate and Regulatory Matters (Narrative-Missouri) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) mi
Ameren Transmission Company of Illinois [Member] | Mark Twain Project [Member]
Public Utilities, General Disclosures [Line Items]
Transmission Line Miles | mi	95
Pending Rate Case [Member] | Union Electric Company | Electric Distribution
Public Utilities, General Disclosures [Line Items]
Revenue Requirement	$ 3,400
Public Utilities, Requested Rate Increase (Decrease), Amount	92
Components of Rate Increase - Net Energy Costs [Member] | Union Electric Company | Electric Distribution
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	54
Components of Rate Increase - Regulatory Amortizations [Member] | Union Electric Company | Electric Distribution
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	26
Final Rate Order | Union Electric Company | MEEIA | Electric Distribution
Public Utilities, General Disclosures [Line Items]
Incentive Award if Energy Efficiency Goals Are Achieved	$ 28