| Standard label: | Class of Treasury Stock [Table Text Block] |
| Name: | us-gaap:ScheduleOfTreasuryStockByClassTextBlock |
| Documentation: | Tabular disclosure of treasury stock, including, but not limited to, average cost per share, description of share repurchase program, shares repurchased, shares held for each class of treasury stock. |
| Object type: | cm:Level3TextBlock |
| Data type: | Text Block (HTML) (nonnum:textBlockItemType) |
| Period type: | For Period (duration) |
| Balance type: | (no balance type) |
| Abstract: | false |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:ScheduleOfTreasuryStockByClassTextBlock |
| Examples of this text block disclosure: | ClassOfTreasuryStock |
| Label | Role | Language |
| Class of Treasury Stock [Table Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 505 30 45 1 | http://fasb.org/us-gaap/role/ref/legacyRef | 505 |
| FASB Accounting Standards Codification 505 30 50 2 | http://fasb.org/us-gaap/role/ref/legacyRef | 505 |
| FASB Accounting Standards Codification 505 30 50 3 | http://fasb.org/us-gaap/role/ref/legacyRef | 505 |
| FASB Accounting Standards Codification 505 30 50 4 | http://fasb.org/us-gaap/role/ref/legacyRef | 505 |