| Standard label: | Fair Value Measurements, Nonrecurring [Table Text Block] |
| Name: | us-gaap:FairValueAssetsMeasuredOnNonrecurringBasisTextBlock |
| Documentation: | Tabular disclosure of assets and liabilities by class, including financial instruments measured at fair value that are classified in shareholders' equity, if any, that are measured at fair value on a nonrecurring basis in periods after initial recognition (for example, impaired assets). Disclosures may include, but are not limited to: (a) the fair value measurements recorded and the reasons for the measurements and (b) the level within the fair value hierarchy in which the fair value measurements are categorized in their entirety (levels 1, 2, 3). |
| 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:FairValueAssetsMeasuredOnNonrecurringBasisTextBlock |
| Label | Role | Language |
| Fair Value Measurements, Nonrecurring [Table Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 820 10 50 2 (a) | http://fasb.org/us-gaap/role/ref/legacyRef | 820 |
| FASB Accounting Standards Codification 820 10 50 2 (b) | http://fasb.org/us-gaap/role/ref/legacyRef | 820 |
| FASB Accounting Standards Codification 820 10 50 2 (bbb) | http://fasb.org/us-gaap/role/ref/legacyRef | 820 |