cm:Level3TextBlock: us-gaap:ShortdurationInsuranceContractsClaimsDevelopmentTableTextBlock
| Short-duration Insurance Contracts, Claims Development [Table Text Block] |
| us-gaap:ShortdurationInsuranceContractsClaimsDevelopmentTableTextBlock |
| Tabular disclosure of undiscounted information about claims development by accident year for short-duration insurance contracts. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ShortdurationInsuranceContractsClaimsDevelopmentTableTextBlock |