cm:Concept: us-gaap:FairValueOptionReasonsForPartialElection
| Fair Value, Option, Reasons for Partial Election |
| us-gaap:FairValueOptionReasonsForPartialElection |
| Where the fair value option is elected for some but not all eligible items within a group of similar eligible items, this item represents a description of those similar items and the reasons for partial election. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:FairValueOptionReasonsForPartialElection |