cm:Level3TextBlock: us-gaap:ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTableTextBlock
| Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table Text Block] |
| us-gaap:ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTableTextBlock |
| Tabular disclosure for the reconciliation of claims development to the liability for unpaid claims and claim adjustment expense for short-duration insurance contracts. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ShortdurationInsuranceContractsReconciliationOfClaimsDevelopmentToLiabilityTableTextBlock |