cm:Concept: us-gaap:AssetAtFairValueChangesInFairValueResultingFromChangesInAssumptions
| Asset at Fair Value, Changes in Fair Value Resulting from Changes in Assumptions |
| us-gaap:AssetAtFairValueChangesInFairValueResultingFromChangesInAssumptions |
| Amount of increase (decrease) in fair value from changes in the assumptions or model used to calculate the fair value of a contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:AssetAtFairValueChangesInFairValueResultingFromChangesInAssumptions |