cm:Concept: us-gaap:CommonStockHeldBySubsidiary
| Common Stock Held by Subsidiary |
| us-gaap:CommonStockHeldBySubsidiary |
| Value of entity shares held by subsidiary, which are purchased for the purpose of granting the shares to senior employees as part of an employee stock option plan approved by the Entity's Board of Directors. Presented as a reduction of shareholders' equity at their cost to the subsidiary. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Debit |
| false |
| us-gaap:CommonStockHeldBySubsidiary |