cm:Concept: us-gaap:ShortdurationInsuranceContractsIncurredButNotReportedIbnrClaimsMethodologies
| Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims, Methodologies |
| us-gaap:ShortdurationInsuranceContractsIncurredButNotReportedIbnrClaimsMethodologies |
| Description of methodologies and changes in methodologies used in determining incurred-but-not-reported (IBNR) liabilities and expected development on reported claims for short-duration insurance contracts. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ShortdurationInsuranceContractsIncurredButNotReportedIbnrClaimsMethodologies |