cm:Concept: us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions
| Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Additions |
| us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions |
| Amount of additions to the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans 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:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAdditions |