cm:Concept: us-gaap:FairValueOptionRelationToBalanceSheetPartialElection
| Fair Value, Option, Relation to Balance Sheet, Partial Election |
| us-gaap:FairValueOptionRelationToBalanceSheetPartialElection |
| Where the fair value option is elected for some but not all eligible items within a group of similar eligible items, this item represents information to enable users to understand how the group of similar items relates to individual line items on the statement of financial position. |
| cm:Concept |
| Text/String (xbrli:stringItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:FairValueOptionRelationToBalanceSheetPartialElection |