cm:Concept: us-gaap:OwnshareLendingArrangementCounterpartyDefaultEarningsPerShareShares
| Own-share Lending Arrangement, Counterparty Default, Earnings Per Share, Shares |
| us-gaap:OwnshareLendingArrangementCounterpartyDefaultEarningsPerShareShares |
| In periods in which default, by a counterparty (share borrower) to a share-lending arrangement, is probable, but has not yet occurred, this item represents the number of the entity's shares related to the share-lending arrangement that will be reflected in basic and diluted earnings per share when the counterparty (share borrower) default does occur. |
| cm:Concept |
| Shares (xbrli:sharesItemType) |
| As Of (instant) |
| (no balance type) |
| false |
| us-gaap:OwnshareLendingArrangementCounterpartyDefaultEarningsPerShareShares |