cm:Concept: us-gaap:DebtSecuritiesAvailableForSaleChangeInPresentValueExpenseReversal
| Debt Securities, Available-for-sale, Change in Present Value, Expense (Reversal) |
| us-gaap:DebtSecuritiesAvailableForSaleChangeInPresentValueExpenseReversal |
| Amount of expense (reversal of expense) for expected credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), from change in present value of expected cash flows. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleChangeInPresentValueExpenseReversal |