| Document and Entity Information Document | Feb. 09, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 9, 2021 |
| Entity Registrant Name | Commerce Bancshares, Inc. |
| Entity Incorporation, State or Country Code | MO |
| Entity File Number | 0-2989 |
| Entity Tax Identification Number | 43-0889454 |
| Entity Address, Address Line One | 1000 Walnut, |
| Entity Address, City or Town | Kansas City, |
| Entity Address, State or Province | MO |
| Entity Address, Postal Zip Code | 64106 |
| City Area Code | 816 |
| Local Phone Number | 234-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | $5 Par Value Common Stock |
| Trading Symbol | CBSH |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0000022356 |
