cm:Concept: us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsGrossIncurredLoss1
| Liability for Asbestos and Environmental Claims, Gross, Incurred Loss |
| us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsGrossIncurredLoss1 |
| Amount, before effects of reinsurance, of expense for claims incurred and costs incurred in the claim settlement process attributable to asbestos and environmental claims. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsGrossIncurredLoss1 |