cm:Concept: us-gaap:ProceedsAndExcessTaxBenefitFromSharebasedCompensation
| Proceeds and Excess Tax Benefit from Share-based Compensation |
| us-gaap:ProceedsAndExcessTaxBenefitFromSharebasedCompensation |
| The aggregate cash inflow comprised of the amount received from (a) employees to acquire the entity's shares under incentive awards, including stock option exercises and restricted stock arrangements, and (b) the excess tax benefit arising from such transactions. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ProceedsAndExcessTaxBenefitFromSharebasedCompensation |