cm:Concept: us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsNetPaymentForClaims
| Liability for Asbestos and Environmental Claims, Net, Payment for Claims |
| us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsNetPaymentForClaims |
| Amount, after effects of reinsurance, of payments to settle insured claims and pay costs incurred in the claims settlement process attributable to asbestos and environmental claims. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:LiabilityForAsbestosAndEnvironmentalClaimsNetPaymentForClaims |