cm:Concept: us-gaap:ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleAmountOfImpairmentLoss
| Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss |
| us-gaap:ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleAmountOfImpairmentLoss |
| Loss recognized as a result of the initial and subsequent write-down of a long-lived asset's carrying amount to fair value. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ImpairedAssetsToBeDisposedOfByMethodOtherThanSaleAmountOfImpairmentLoss |