cm:Concept: us-gaap:StockholdersEquityNoteImpactOfConversionOfContingentlyConvertibleSecuritiesOnDilutedEarningsPerShare
| Stockholders' Equity Note, Impact of Conversion of Contingently Convertible Securities on Diluted Earnings Per Share |
| us-gaap:StockholdersEquityNoteImpactOfConversionOfContingentlyConvertibleSecuritiesOnDilutedEarningsPerShare |
| Description of reason for including or excluding share issuable in conversion of contingently convertible security in calculation of diluted earnings per share. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:StockholdersEquityNoteImpactOfConversionOfContingentlyConvertibleSecuritiesOnDilutedEarningsPerShare |