cm:Concept: us-gaap:OwnshareLendingArrangementCounterpartyDefaultChangesInValueRecoveries
| Own-share Lending Arrangement, Counterparty Default, Changes in Value, Probable Recoveries |
| us-gaap:OwnshareLendingArrangementCounterpartyDefaultChangesInValueRecoveries |
| This item represents, in periods subsequent to the period in which the entity concludes it is probable that the counterparty (share borrower) to a share-lending arrangement will default, the change in the amount of probable recoveries which the entity has recognized in earnings for the period. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:OwnshareLendingArrangementCounterpartyDefaultChangesInValueRecoveries |