cm:Concept: us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOtherDescription
| Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Other, Description |
| us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOtherDescription |
| Description of reason for increase (decrease), classified as other, in number of awards under share-based payment arrangement. Excludes share and unit options. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOtherDescription |