cm:Concept: us-gaap:DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
| Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment |
| us-gaap:DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments |
| Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments |