cm:Concept: us-gaap:DefinedBenefitPlanNarrativeDescriptionOfBasisUsedToDetermineOverallExpectedLongTermRateOfReturnOnAssetsAssumption
| Defined Benefit Plan, Plan Assets, Expected Long-term Rate-of-Return, Description |
| us-gaap:DefinedBenefitPlanNarrativeDescriptionOfBasisUsedToDetermineOverallExpectedLongTermRateOfReturnOnAssetsAssumption |
| Description of basis used to determine overall expected long-term rate-of-return assumption for plan asset of defined benefit plan. Includes, but is not limited to, approach used, and extent approach was based on historical return and adjustment made to reflect expectation of future return. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DefinedBenefitPlanNarrativeDescriptionOfBasisUsedToDetermineOverallExpectedLongTermRateOfReturnOnAssetsAssumption |