cm:Member: us-gaap:WorkforceSubjectToCollectiveBargainingArrangementsExpiringWithinOneYearMember
| Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] |
| us-gaap:WorkforceSubjectToCollectiveBargainingArrangementsExpiringWithinOneYearMember |
| The number of employees covered by a collective bargaining agreement that will expire within one year after 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:WorkforceSubjectToCollectiveBargainingArrangementsExpiringWithinOneYearMember |