cm:Concept: us-gaap:DefinedBenefitPlanNetPeriodicBenefitCostPracticalExpedientComparativePeriodDisclosure
| Defined Benefit Plan, Net Periodic Benefit Cost, Practical Expedient, Comparative Period Disclosure [true false] |
| us-gaap:DefinedBenefitPlanNetPeriodicBenefitCostPracticalExpedientComparativePeriodDisclosure |
| Indicates (true false) whether practical expedient was elected to use amounts for net periodic benefit cost components, disclosed in pension and other postretirement benefit plan note, for prior comparative period in statement of income or comprehensive income. |
| cm:Concept |
| Yes/No (xbrli:booleanItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DefinedBenefitPlanNetPeriodicBenefitCostPracticalExpedientComparativePeriodDisclosure |