cm:Concept: us-gaap:ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod
| Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method |
| us-gaap:ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod |
| Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod |