| Standard label: | Credit Loss, Financial Instrument [Policy Text Block] |
| Name: | us-gaap:CreditLossFinancialInstrumentPolicyTextBlock |
| Documentation: | Disclosure of accounting policy for credit loss on financial instrument measured at amortized cost basis, net investment in lease, off-balance sheet credit exposure, and available-for-sale debt security. Includes, but is not limited to, methodology used to estimate allowance for credit loss, how writeoff of uncollectible amount is recognized, and determination of past due status and nonaccrual status. |
| Object type: | cm:Level2TextBlock |
| 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:CreditLossFinancialInstrumentPolicyTextBlock |
| Label | Role | Language |
| Credit Loss, Financial Instrument [Policy Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 326 20 50 11 | http://www.xbrl.org/2003/role/disclosureRef | 326 |
| FASB Accounting Standards Codification 326 20 50 14 | http://www.xbrl.org/2003/role/disclosureRef | 326 |
| FASB Accounting Standards Codification 326 20 50 17 | http://www.xbrl.org/2003/role/disclosureRef | 326 |
| FASB Accounting Standards Codification 326 20 50 21 | http://www.xbrl.org/2003/role/disclosureRef | 326 |
| FASB Accounting Standards Codification 326 30 50 7 | http://www.xbrl.org/2003/role/disclosureRef | 326 |