cm:Level3TextBlock: us-gaap:ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock
| Share-based Payment Arrangement, Option, Activity [Table Text Block] |
| us-gaap:ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock |
| Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock |
| SharebasedCompensationStockOptionsActivity |