cm:Concept: us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossNoncurrent
| Debt Securities, Available-for-sale, Allowance for Credit Loss, Noncurrent |
| us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossNoncurrent |
| Amount of 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), classified as noncurrent. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Credit |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossNoncurrent |