| Standard label: | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Including Noncontrolling Interest [Member] |
| Name: | us-gaap:AccumulatedNetInvestmentGainLossIncludingPortionAttributableToNoncontrollingInterestMember |
| Documentation: | Accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), including portion attributable to noncontrolling interest. |
| Object type: | cm:Member |
| Data type: | [Member] (nonnum:domainItemType) |
| Period type: | For Period (duration) |
| Balance type: | (no balance type) |
| Abstract: | true |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:AccumulatedNetInvestmentGainLossIncludingPortionAttributableToNoncontrollingInterestMember |
| Label | Role | Language |
| AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Including Noncontrolling Interest [Member] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 220 10 45 10A (e) | http://www.xbrl.org/2003/role/disclosureRef | 220 |
| FASB Accounting Standards Codification 220 10 45 10A (f) | http://www.xbrl.org/2003/role/disclosureRef | 220 |
| FASB Accounting Standards Codification 220 10 45 10A (h) | http://www.xbrl.org/2003/role/disclosureRef | 220 |
| FASB Accounting Standards Codification 220 10 45 17B | http://www.xbrl.org/2003/role/disclosureRef | 220 |
| FASB Accounting Standards Codification 220 10 45 14A | http://www.xbrl.org/2003/role/disclosureRef | 220 |