cm:Concept: us-gaap:PremiumsWrittenAndEarnedMethodologyAndAssumptions
| Premiums Written and Earned, Methodology and Assumptions |
| us-gaap:PremiumsWrittenAndEarnedMethodologyAndAssumptions |
| Methodology and assumptions regarding premiums written and earned directly by insurer for all insurance and before adding contracts assumed from other insurers or subtracting any amounts ceded to other insurers. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:PremiumsWrittenAndEarnedMethodologyAndAssumptions |