cm:Concept: us-gaap:AmountOfDilutiveSecuritiesESOPConvertiblePreferredStock
| Dilutive Securities, Effect on Basic Earnings Per Share, ESOP Convertible Preferred Stock |
| us-gaap:AmountOfDilutiveSecuritiesESOPConvertiblePreferredStock |
| Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of convertible preferred stock of an employee stock ownership plan (ESOP). |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:AmountOfDilutiveSecuritiesESOPConvertiblePreferredStock |