cm:Concept: us-gaap:GrandfatheredESOPExpenseRecognitionActualInterestIncurredOnESOPDebt
| Grandfathered ESOP Expense Recognition, Actual Interest Incurred on ESOP Debt |
| us-gaap:GrandfatheredESOPExpenseRecognitionActualInterestIncurredOnESOPDebt |
| For grandfathered ESOP shares acquired prior to January 1, 1993, the actual interest incurred on debt for obligations that the employer may secure on behalf of the ESOP. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:GrandfatheredESOPExpenseRecognitionActualInterestIncurredOnESOPDebt |