cm:Concept: us-gaap:PreferredStockRedemptionDiscount
| Preferred Stock Redemption Discount |
| us-gaap:PreferredStockRedemptionDiscount |
| The excess of (1) the carrying amount of the preferred stock in the registrant's balance sheet over (2) the fair value of the consideration transferred to the holders of the preferred stock, during the accounting period, which will be added to net earnings to arrive at net earnings available to common shareholders in the calculation of earnings per share. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:PreferredStockRedemptionDiscount |