cm:Concept: us-gaap:UndistributedEarningsLossFromContinuingOperationsAvailableToCommonShareholdersBasic
| Undistributed Earnings (Loss) from Continuing Operations Available to Common Shareholders, Basic |
| us-gaap:UndistributedEarningsLossFromContinuingOperationsAvailableToCommonShareholdersBasic |
| Amount of undistributed earnings (loss) from continuing operations allocated to common stock as if earnings had been distributed. Excludes distributed earnings. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Credit |
| false |
| us-gaap:UndistributedEarningsLossFromContinuingOperationsAvailableToCommonShareholdersBasic |