cm:Concept: us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfMortgageBackedSecuritiesMBS
| Proceeds from Maturities, Prepayments and Calls of Mortgage Backed Securities (MBS) |
| us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfMortgageBackedSecuritiesMBS |
| The cash inflow from the maturity (principal due), prepayment and call (request of early payment) of a loan financed by home mortgage payments classified as held to maturity. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ProceedsFromMaturitiesPrepaymentsAndCallsOfMortgageBackedSecuritiesMBS |