cm:Concept: us-gaap:AccrualForEnvironmentalLossContingenciesMaterialChangesInAccrual
| Accrual for Environmental Loss Contingencies, Material Changes in Accrual |
| us-gaap:AccrualForEnvironmentalLossContingenciesMaterialChangesInAccrual |
| Explanation of material changes in the expected aggregate amount of the environmental loss contingencies obligation since the prior balance sheet date, other than those resulting from the pay-down of the obligation. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:AccrualForEnvironmentalLossContingenciesMaterialChangesInAccrual |