cm:Concept: us-gaap:ParticipatingSecuritiesDistributedAndUndistributedEarningsLossDiluted
| Participating Securities, Distributed and Undistributed Earnings (Loss), Diluted |
| us-gaap:ParticipatingSecuritiesDistributedAndUndistributedEarningsLossDiluted |
| Amount of earnings (loss) distributed and earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method. |
| cm:Concept |
| Monetary (xbrli:monetaryItemType) |
| For Period (duration) |
| Debit |
| false |
| us-gaap:ParticipatingSecuritiesDistributedAndUndistributedEarningsLossDiluted |