cm:Concept: us-gaap:AcceleratedShareRepurchasesAdjustmentToRecordedAmount
| Accelerated Share Repurchases, Adjustment to Recorded Amount |
| us-gaap:AcceleratedShareRepurchasesAdjustmentToRecordedAmount |
| The adjustment needed to reconcile previously recorded amounts to the actual aggregate amount paid, whether in cash or other consideration, to acquire all of the shares purchased under an Accelerated Share Repurchase arrangement. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:AcceleratedShareRepurchasesAdjustmentToRecordedAmount |