cm:Concept: us-gaap:LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
| Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans |
| us-gaap:LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans |
| Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period). |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans |