| Document and Entity Information | Dec. 02, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | AMEREN CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0001002910 |
| Document Type | 8-K |
| Document Period End Date | Dec. 2, 2019 |
| Entity Incorporation State Country Code | MO |
| Entity File Number | 1-14756 |
| Entity Tax Identification Number | 43-1723446 |
| Entity Address, Address Line One | 1901 Chouteau Avenue |
| Entity Address, City or Town | St. Louis |
| Entity Address, State or Province | MO |
| Entity Address, Postal Zip Code | 63103 |
| City Area Code | (314) |
| Local Phone Number | 621-3222 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $0.01 par value per share |
| Trading Symbol | AEE |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
