cm:Concept: us-gaap:IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights
| Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights |
| us-gaap:IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights |
| This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method. |
| cm:Concept |
| Shares (xbrli:sharesItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:IncrementalCommonSharesAttributableToParticipatingNonvestedSharesWithNonForfeitableDividendRights |