Commitments And Contingencies (Asbestos-Related Litigation And Tax Exemptions And Credits) (Details) - Asbestos-Related $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) defendant
Loss Contingencies [Line Items]
Number of defendants | defendant	75
Number of pending asbestos lawsuits as of the balance sheet date	48	[1]
Loss contingency range of possible loss, minimum	$ 8
Percent of allowed cash expenditures in excess of base rates to be recovered through charges assessed to customers	90.00%
Asbestos trust fund balance	$ 22
Percent of difference to be contributed to the asbestos trust fund if cash expenditures are less than amount included in base electric rates.	90.00%
Union Electric Company
Loss Contingencies [Line Items]
Number of pending asbestos lawsuits as of the balance sheet date	26
Loss contingency range of possible loss, minimum	$ 3
Ameren Illinois Company
Loss Contingencies [Line Items]
Number of pending asbestos lawsuits as of the balance sheet date	38
Loss contingency range of possible loss, minimum	$ 5

[1] (a)Total does not equal the sum of the subsidiary unit lawsuits because some of the lawsuits name multiple Ameren entities as defendants.