cm:Concept: us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldTransfersToLoansHeldForSale
| Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Transfers to Loans Held-for-sale |
| us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldTransfersToLoansHeldForSale |
| Amount of reduction, resulting from a reclassification to held-for-sale, in 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) |
| Credit |
| false |
| us-gaap:CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldTransfersToLoansHeldForSale |