cm:Concept: us-gaap:BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain
| Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain |
| us-gaap:BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain |
| In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain |