cm:Level3TextBlock: us-gaap:DefinedBenefitPlanPlanAssetsCategoryTableTextBlock
| Defined Benefit Plan, Plan Assets, Category [Table Text Block] |
| us-gaap:DefinedBenefitPlanPlanAssetsCategoryTableTextBlock |
| Tabular disclosure of defined benefit plan asset investment. Includes, but is not limited to, fair value of category of plan asset and its level within fair value hierarchy. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DefinedBenefitPlanPlanAssetsCategoryTableTextBlock |