cm:Level3TextBlock: us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock
| Schedule of Available-for-sale Securities Reconciliation [Table Text Block] |
| us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock |
| Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. |
| cm:Level3TextBlock |
| Text Block (HTML) (nonnum:textBlockItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock |
| AvailableForsaleSecuritiesReconciliation |