cm:Concept: us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities
| Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities |
| us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities |
| The cash inflow associated with the maturity, prepayments and calls (requests for early payments) of debt securities designated as held-to-maturity. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities |