cm:Concept: us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationDescriptionAndTerms
| Share-based Compensation Arrangement by Share-based Payment Award, Plan Modification, Description and Terms |
| us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationDescriptionAndTerms |
| Description of modification of award under share-based payment arrangement. Includes, but is not limited to, terms for expiration date, vesting rights and exercise price. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationDescriptionAndTerms |