cm:Concept: us-gaap:DebtSecuritiesAvailableForSaleChangeInValuationTechnique
| Debt Securities, Available-for-sale, Change in Valuation Technique [true false] |
| us-gaap:DebtSecuritiesAvailableForSaleChangeInValuationTechnique |
| Indicates (true false) whether valuation technique or approach changed for measuring investment in debt security at fair value with change in fair value recognized in other comprehensive income (available-for-sale). |
| cm:Concept |
| Yes/No (xbrli:booleanItemType) |
| As Of (instant) |
| (no balance type) |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleChangeInValuationTechnique |