| Standard label: | External Credit Rating by Grouping [Axis] |
| Name: | us-gaap:ExternalCreditRatingByGroupingAxis |
| Documentation: | Information by external rating classified as investment grade or non investment grade. |
| Object type: | cm:Axis |
| Data type: | Text/String (xbrli:stringItemType) |
| Period type: | For Period (duration) |
| Balance type: | (no balance type) |
| Abstract: | true |
| Workiva Wdesk Taxonomy Analyzer: | us-gaap:ExternalCreditRatingByGroupingAxis |
| Label | Role | Language |
| External Credit Rating by Grouping [Axis] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 310 10 50 29 | http://fasb.org/us-gaap/role/ref/legacyRef | 310 |
| FASB Accounting Standards Codification 326 20 50 5 | http://www.xbrl.org/2009/role/commonPracticeRef | 326 |
| FASB Accounting Standards Codification 460 10 50 4 (a)(4) | http://www.xbrl.org/2003/role/exampleRef | 460 |
| FASB Accounting Standards Codification 815 10 50 4K (a)(4) | http://www.xbrl.org/2003/role/disclosureRef | 815 |