| Standard label: | Debt Securities, Available-for-sale, Realized Gain (Loss) |
| Name: | us-gaap:DebtSecuritiesAvailableForSaleRealizedGainLoss |
| Documentation: | Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). |
| Object type: | cm:Concept |
| Data type: | Monetary (xbrli:monetaryItemType) |
| Period type: | For Period (duration) |
| Balance type: | Credit |
| Abstract: | false |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:DebtSecuritiesAvailableForSaleRealizedGainLoss |
| Label | Role | Language |
| Debt Securities, Available-for-sale, Realized Gain (Loss) | http://www.xbrl.org/2003/role/label | en-US |
| Debt Securities, Available-for-sale, Realized Gain (Loss), Total | http://www.xbrl.org/2003/role/totalLabel | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 320 10 50 9 (a) | http://www.xbrl.org/2009/role/commonPracticeRef | 320 |
| Part Of Roll Up: |
| us-gaap:DebtSecuritiesRealizedGainLoss |
| us-gaap:DebtSecuritiesAvailableForSaleGainLoss |