cm:Level3TextBlock: us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossTableTextBlock
| Debt Securities, Available-for-sale, Allowance for Credit Loss [Table Text Block] |
| us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossTableTextBlock |
| Tabular disclosure 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). |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleAllowanceForCreditLossTableTextBlock |