cm:Level2TextBlock: us-gaap:PropertyLiabilityReserveEstimatePolicy
| Property Liability Reserve Estimate, Policy [Policy Text Block] |
| us-gaap:PropertyLiabilityReserveEstimatePolicy |
| Disclosure of accounting policy amounts needed to provide for the estimated ultimate cost of settling property insurance claims relating to insured events that have occurred on or before a particular date (ordinarily, the statement of financial position date). |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:PropertyLiabilityReserveEstimatePolicy |