cm:Member: us-gaap:WorkforceSubjectToCollectiveBargainingArrangementsMember
| Workforce Subject to Collective Bargaining Arrangements [Member] |
| us-gaap:WorkforceSubjectToCollectiveBargainingArrangementsMember |
| The number of employees covered by a collective bargaining agreement as of the balance sheet date, when it serves as a benchmark in a concentration of risk calculation. |
| cm:Member |
| [Member] (nonnum:domainItemType) |
| For Period (duration) |
| (no balance type) |
| true |
| us-gaap:WorkforceSubjectToCollectiveBargainingArrangementsMember |