cm:Concept: us-gaap:DescriptionOfPostretirementMedicalPlansWithPrescriptionDrugBenefits
| Defined Benefit Plan, Postretirement Medical Plan with Prescription Drug Benefits, Description |
| us-gaap:DescriptionOfPostretirementMedicalPlansWithPrescriptionDrugBenefits |
| Description of postretirement medical plan with prescription drug coverage and existence of Medicare Prescription Drug, Improvement and Modernization Act of 2003. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DescriptionOfPostretirementMedicalPlansWithPrescriptionDrugBenefits |