Commitments And Contingencies (Asbestos-Related Litigation And Tax Exemptions And Credits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended							1 Months Ended
	Dec. 31, 2013 Asbestos-Related defendant		Dec. 31, 2013 Parent Company Asbestos-Related	Dec. 31, 2013 Union Electric Company Asbestos-Related	Dec. 31, 2013 Ameren Illinois Company Asbestos-Related	Dec. 31, 2013 Ameren Illinois Company Collectibility of Taxes	Dec. 31, 2012 Ameren Illinois Company Collectibility of Taxes customer	Sep. 30, 2013 State Ameren Illinois Company Collectibility of Taxes	Jul. 31, 2013 State Ameren Illinois Company Collectibility of Taxes
Loss Contingencies [Line Items]
Number of defendants	82
Number of pending asbestos lawsuits as of the balance sheet date	71,000,000	[1]	1,000,000	47,000,000	50,000,000
Percent of allowed cash expenditures in excess of base rates to be recovered through charges assessed to customers	90.00%
Asbestos trust fund balance	$ 23
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%
Number of customers affected							2,400
Loss Contingency, Damages Awarded, Value								0.5	4.0
Loss contingency range of possible loss, minimum	11.0			5.0	6.0	1.0
Loss contingency range of possible loss, maximum						5.0
Loss Contingency Accrual, at Carrying Value						$ 1

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