cm:Concept: us-gaap:IncomeTaxEffectsAllocatedDirectlyToEquityEmployeeStockOptions
| Income Tax Effects Allocated Directly to Equity, Employee Stock Options |
| us-gaap:IncomeTaxEffectsAllocatedDirectlyToEquityEmployeeStockOptions |
| The tax effects of employee stock option transactions that are recognized differently for financial reporting and tax purposes, occurring during the period and charged or credited directly to shareholders' equity. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:IncomeTaxEffectsAllocatedDirectlyToEquityEmployeeStockOptions |