Summary Of Significant Accounting Policies (Schedule Of Rates Used For Allowance For Funds Used During Construction) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Union Electric Company
Accounting Policies [Line Items]
Allowance for funds used during construction, rate	7.00%	7.00%	7.00%
Ameren Illinois Company
Accounting Policies [Line Items]
Allowance for funds used during construction, rate	4.00%	5.00%	6.00%

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

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