Summary Of Significant Accounting Policies (Schedule Of Excise Taxes) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Line Items]
Excise tax expense	$ 213	$ 193	$ 194
Union Electric Company
Accounting Policies [Line Items]
Excise tax expense	152	139	137
Ameren Illinois Company
Accounting Policies [Line Items]
Excise tax expense	$ 61	$ 54	$ 57