Summary Of Significant Accounting Policies (Schedule Of Excise Taxes) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Line Items]
Excise tax expense	$ 215	$ 213	$ 193
Union Electric Company
Accounting Policies [Line Items]
Excise tax expense	151	152	139
Ameren Illinois Company
Accounting Policies [Line Items]
Excise tax expense	$ 64	$ 61	$ 54