cm:Concept: us-gaap:LoansReceivableHeldForSaleReconciliationToCashFlowDeductionsFromHeldForSale
| Loans Receivable Held-for-sale, Reconciliation to Cash Flow, Deductions from Held-for-sale |
| us-gaap:LoansReceivableHeldForSaleReconciliationToCashFlowDeductionsFromHeldForSale |
| Amount, after allowance for bad debt, of deductions to loan receivables held-for-sale that are not part of a disposal group. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:LoansReceivableHeldForSaleReconciliationToCashFlowDeductionsFromHeldForSale |