cm:Level2TextBlock: us-gaap:LiabilityReserveEstimatePolicy
| Liability Reserve Estimate, Policy [Policy Text Block] |
| us-gaap:LiabilityReserveEstimatePolicy |
| Disclosure of accounting policy for estimating its liability as of the balance sheet date for the ultimate cost of settling reported and unreported claims incurred and claims adjustment expenses (including effects of inflation and other societal and economic factors). |
| cm:Level2TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:LiabilityReserveEstimatePolicy |