cm:Concept: us-gaap:ContingentlyConvertibleSecuritiesIncludedInDilutedEarningsPerShare
| Contingently Convertible Securities Included in Diluted Earnings Per Share [true false] |
| us-gaap:ContingentlyConvertibleSecuritiesIncludedInDilutedEarningsPerShare |
| Indicates (true false) whether share issuable in conversion of contingently convertible security is included in calculation of diluted earnings per share. |
| cm:Concept |
| Yes/No (xbrli:booleanItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ContingentlyConvertibleSecuritiesIncludedInDilutedEarningsPerShare |