cm:Concept: us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherShareIncreaseDecrease
| Share-based Compensation Arrangement by Share-based Payment Award, Other Share Increase (Decrease) |
| us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherShareIncreaseDecrease |
| Other than shares newly issued, the number of additional shares issued (for example, a stock split) or canceled (for example, to correct a share issuance), during the period under the plan. |
| cm:Concept |
| Shares (xbrli:sharesItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherShareIncreaseDecrease |