cm:Level3TextBlock: us-gaap:ScheduleOfRentExpenseTableTextBlock
| Schedule of Rent Expense [Table Text Block] |
| us-gaap:ScheduleOfRentExpenseTableTextBlock |
| Tabular disclosure of rental expense from operating leases for each period for which an income statement is presented with separate amounts for minimum rentals, contingent rentals, and sublease rentals. Rental payments under leases with terms of a month or less that were not renewed need not be included. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ScheduleOfRentExpenseTableTextBlock |
| OperatingLeasesRentExpenseNetRollUp |