cm:Concept: us-gaap:CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseDescription
| Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Description |
| us-gaap:CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseDescription |
| Description of the reasons for the change in incurred claims and claim adjustment expenses recognized in the income statement attributable to insured events of prior fiscal years. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseDescription |