cm:LineItems: us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |
| us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems |
| Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. |
| cm:LineItems |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| true |
| us-gaap:AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems |