Document And Entity Information	3 Months Ended
	Mar. 31, 2012	Apr. 30, 2012
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Trading Symbol	AEE
Entity Registrant Name	AMEREN CORP
Entity Central Index Key	0001002910
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Ameren Corporation [Member]
Entity Common Stock, Shares Outstanding		242,634,671
Union Electric Company [Member]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Entity Registrant Name	UNION ELECTRIC CO
Entity Central Index Key	0000100826
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		102,123,834
Ameren Illinois Company [Member]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Entity Registrant Name	AMEREN ILLINOIS CO
Entity Central Index Key	0000018654
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		25,452,373
Ameren Energy Generating Company [Member]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Entity Registrant Name	AMEREN ENERGY GENERATING CO
Entity Central Index Key	0001135361
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		2,000