cm:Concept: us-gaap:IncrementalCommonSharesAttributableToEquityForwardAgreements
| Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements |
| us-gaap:IncrementalCommonSharesAttributableToEquityForwardAgreements |
| Additional shared included in the calculation of diluted EPS as a result of the potentially dilutive effect of equity forward arrangements using the reverse treasury stock method. |
| cm:Concept |
| Shares (xbrli:sharesItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:IncrementalCommonSharesAttributableToEquityForwardAgreements |