Entity Shell Company Entity Shell Company Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Entity Public Float Entity Public Float Auditor Name Auditor Name ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Amendment Flag Amendment Flag Auditor Location Auditor Location Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Ameren Missouri Union Electric Company [Member] Union Electric Company Emerging growth company Entity Emerging Growth Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Current Reporting Status Entity Current Reporting Status Entity File Number Entity File Number Entity Small Business Entity Small Business Document Financial Statement Error Correction [Flag] Document Financial Statement Error Correction [Flag] Auditor Firm ID Auditor Firm ID Entity Address, State or Province Entity Address, State or Province Document Transition Report Document Transition Report Entity Address, Address Line One Entity Address, Address Line One City Area Code City Area Code Document Fiscal Period Focus Document Fiscal Period Focus Entity Voluntary Filers Entity Voluntary Filers Cover [Abstract] Cover [Abstract] Entity Information [Line Items] Entity Information [Line Items] Document Period End Date Document Period End Date Document Information [Table] Document Information [Table] Current Fiscal Year End Date Current Fiscal Year End Date Entity Central Index Key Entity Central Index Key Legal Entity [Axis] Legal Entity [Axis] Entity Tax Identification Number Entity Tax Identification Number Document Annual Report Document Annual Report Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Registrant Name Entity Registrant Name Entity [Domain] Entity [Domain] Document Fiscal Year Focus Document Fiscal Year Focus Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Address, City or Town Entity Address, City or Town Document Type Document Type Entity Interactive Data Current Entity Interactive Data Current