cm:Level1TextBlock: us-gaap:SubsequentEventProFormaBusinessCombinations
| Subsequent Event, Pro Forma Business Combinations or Disposals [Text Block] |
| us-gaap:SubsequentEventProFormaBusinessCombinations |
| The entire disclosure for pro forma information for significant acquisitions or disposals that occurred or are probable to occur after the balance sheet date. |
| cm:Level1TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:SubsequentEventProFormaBusinessCombinations |
| SubsequentEventProFormaBusinessCombinationsDisclosure |