cm:Concept: us-gaap:JuniorSubordinatedLongTermNotes
| Junior Subordinated Notes, Noncurrent |
| us-gaap:JuniorSubordinatedLongTermNotes |
| Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments, excluding current portion. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| As Of (instant) |
| Credit |
| false |
| us-gaap:JuniorSubordinatedLongTermNotes |