cm:Table: us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable
| Debt Securities, Available-for-sale, Allowance for Credit Loss [Table] |
| us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable |
| Disclosure of information about allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). |
| cm:Table |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| true |
| us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossTable |