cm:Concept: us-gaap:DebtSecuritiesAvailableForSaleMaturityAllocationExtensibleList
| Debt Securities, Available-for-sale, Maturity Allocation [Extensible List] |
| us-gaap:DebtSecuritiesAvailableForSaleMaturityAllocationExtensibleList |
| Indicates methodology used as basis for allocating investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) without single maturity date. |
| cm:Concept |
| srt-types:extensibleListItemType |
| As Of (instant) |
| (no balance type) |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleMaturityAllocationExtensibleList |