cm:Concept: us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesProvisionForLoanLosses1
| Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Provision for Loan Losses |
| us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesProvisionForLoanLosses1 |
| Amount of expense related to loan loss not accounted for as debt securities, with evidence of deterioration of credit quality. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesProvisionForLoanLosses1 |