cm:Concept: us-gaap:DebtSecuritiesAvailableForSaleCostOfSecuritySoldMethodExtensibleList
| Debt Securities, Available-for-sale, Cost of Security Sold, Method [Extensible List] |
| us-gaap:DebtSecuritiesAvailableForSaleCostOfSecuritySoldMethodExtensibleList |
| Indicates method used to determine cost basis of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), sold. Includes, but is not limited to, specific identification or average cost method. |
| cm:Concept |
| srt-types:extensibleListItemType |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleCostOfSecuritySoldMethodExtensibleList |