cm:Level3TextBlock: us-gaap:ScheduleOfShareBasedCompensationStockAppreciationRightsAwardActivityTableTextBlock
| Share-based Payment Arrangement, Stock Appreciation Right, Activity [Table Text Block] |
| us-gaap:ScheduleOfShareBasedCompensationStockAppreciationRightsAwardActivityTableTextBlock |
| Tabular disclosure of the number and weighted-average exercise prices (or conversion ratios) for stock appreciation rights awards that were outstanding at the beginning and end of the year, and the number of stock appreciation rights awards that were granted, exercised or converted, forfeited, and expired during the year. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ScheduleOfShareBasedCompensationStockAppreciationRightsAwardActivityTableTextBlock |
| SharebasedCompensationStockAppreciationRightsAwardActivity |