| Standard label: | Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] |
| Name: | us-gaap:FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock |
| Documentation: | Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset. |
| 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:FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock |
| Examples of this text block disclosure: | FairValueAssetsMeasuredonRecurringBasisUnobservableInputReconciliationCalculationRollForward |
| Label | Role | Language |
| Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 820 10 50 2 (c) | http://fasb.org/us-gaap/role/ref/legacyRef | 820 |
| FASB Accounting Standards Codification 820 10 50 3 | http://fasb.org/us-gaap/role/ref/legacyRef | 820 |