cm:Concept: us-gaap:WeightedAverageNumberOfSharesTreasuryStock
| Weighted Average Number of Shares, Treasury Stock |
| us-gaap:WeightedAverageNumberOfSharesTreasuryStock |
| Number of shares of treasury stock determined by relating the portion of time within a reporting period that treasury shares have been outstanding to the total time in that period. Treasury stock is stock that the Entity has issued but subsequently reacquired. |
| cm:Concept |
| Shares (xbrli:sharesItemType) |
| For Period (duration) |
| (no balance type) |
| false |
| us-gaap:WeightedAverageNumberOfSharesTreasuryStock |