Cover Page - USD ($)
12 Months Ended
Dec. 31, 2019
Jan. 31, 2020
Jun. 28, 2019
Entity Information [Line Items]   
Document Type10-K  
Document Annual Reporttrue  
Document Period End DateDec. 31, 2019  
Document Transition Reportfalse  
Entity File Number1-14756  
Entity Registrant NameAmeren Corporation  
Entity Tax Identification Number43-1723446  
Entity Incorporation, State or Country CodeMO  
Entity Address, Address Line One1901 Chouteau Avenue  
Entity Address, City or TownSt. Louis  
Entity Address, State or ProvinceMO  
Entity Address, Postal Zip Code63103  
City Area Code(314)  
Local Phone Number621-3222  
Title of 12(b) SecurityCommon Stock, $0.01 par value per share  
Trading SymbolAEE  
Security Exchange NameNYSE  
Entity Well-known Seasoned IssuerYes  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryLarge Accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
Entity Shell Companyfalse  
Entity Public Float  $ 18,378,774,986
Entity Common Stock, Shares Outstanding 246,231,712 
Documents Incorporated by ReferencePortions of the definitive proxy statement of Ameren Corporation and portions of the definitive information statements of Union Electric Company and Ameren Illinois Company for the 2020 annual meetings of shareholders are incorporated by reference into Part III of this Form 10-K.   
Entity Central Index Key0001002910  
Current Fiscal Year End Date--12-31  
Document Fiscal Year Focus2019  
Document Fiscal Period FocusFY  
Amendment Flagfalse  
Union Electric Company   
Entity Information [Line Items]   
Entity File Number1-2967  
Entity Registrant NameUnion Electric Company  
Entity Tax Identification Number43-0559760  
Entity Incorporation, State or Country CodeMO  
Entity Address, Address Line One1901 Chouteau Avenue  
Entity Address, City or TownSt. Louis  
Entity Address, State or ProvinceMO  
Entity Address, Postal Zip Code63103  
City Area Code(314)  
Local Phone Number621-3222  
Title of 12(g) SecurityPreferred Stock, cumulative, no par value, stated value $100 per share  
Entity Well-known Seasoned IssuerNo  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding 102,123,834 
Entity Central Index Key0000100826  
Current Fiscal Year End Date--12-31  
Document Fiscal Year Focus2019  
Document Fiscal Period FocusFY  
Amendment Flagfalse  
No Trading Symbol Flagtrue  
Ameren Illinois Company   
Entity Information [Line Items]   
Entity File Number1-3672  
Entity Registrant NameAmeren Illinois Company  
Entity Tax Identification Number37-0211380  
Entity Incorporation, State or Country CodeIL  
Entity Address, Address Line One10 Executive Drive  
Entity Address, City or TownCollinsville  
Entity Address, State or ProvinceIL  
Entity Address, Postal Zip Code62234  
City Area Code(618)  
Local Phone Number343-8150  
Title of 12(g) SecurityPreferred Stock, cumulative, $100 par valueDepositary Shares, each representing 1/4 of a share of 6.625%Preferred Stock, cumulative, $100 par value  
Entity Well-known Seasoned IssuerNo  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding 25,452,373 
Entity Central Index Key0000018654  
Current Fiscal Year End Date--12-31  
Document Fiscal Year Focus2019  
Document Fiscal Period FocusFY  
Amendment Flagfalse  
No Trading Symbol Flagtrue  

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