cm:Abstract: us-gaap:CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldMovementScheduleRollForward
| Certain Loans Acquired in Transfer Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward] |
| us-gaap:CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldMovementScheduleRollForward |
| A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. |
| cm:Abstract |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| true |
| us-gaap:CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldMovementScheduleRollForward |