cm:Level3TextBlock: us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTableTextBlock
| Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block] |
| us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTableTextBlock |
| Tabular disclosure of fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. |
| cm:Level3TextBlock |
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| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionFairValueTableTextBlock |