cm:Concept: us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value |
| us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1 |
| Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1 |