cm:Concept: us-gaap:PaymentsForRepurchaseOfConvertiblePreferredStock
| Payments for Repurchase of Convertible Preferred Stock |
| us-gaap:PaymentsForRepurchaseOfConvertiblePreferredStock |
| The cash outflow to reacquire preferred stock originally issued and identified as a security that can be exchanged for another type of financial security. This repurchased stock is held in treasury. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:PaymentsForRepurchaseOfConvertiblePreferredStock |