cm:Level3TextBlock: us-gaap:DefinedBenefitPlanPlanAssetsAllocationTableTextBlock
| Defined Benefit Plan, Plan Assets, Allocation [Table Text Block] |
| us-gaap:DefinedBenefitPlanPlanAssetsAllocationTableTextBlock |
| Tabular disclosure of investment allocation of defined benefit plan assets. Includes, but is not limited to, investment allocation percentage or range of percentages. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DefinedBenefitPlanPlanAssetsAllocationTableTextBlock |