cm:Concept: us-gaap:IncreaseDecreaseInFinancialInstrumentsUsedInOperatingActivities
| Increase (Decrease) in Financial Instruments Used in Operating Activities |
| us-gaap:IncreaseDecreaseInFinancialInstrumentsUsedInOperatingActivities |
| The increase (decrease) during the reporting period in the aggregate value of financial instruments used in operating activities, including trading securities, risk management instruments, and other short-term trading instruments. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:IncreaseDecreaseInFinancialInstrumentsUsedInOperatingActivities |