cm:Concept: us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions
| Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions |
| us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions |
| Number of investments in debt securities 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:Concept |
| Integer (xbrli:integerItemType) |
| As Of (instant) |
| (no balance type) |
| false |
| us-gaap:DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions |