| Standard label: | Schedule of Capitalized Costs of Unproved Properties Excluded from Amortization [Table Text Block] |
| Name: | us-gaap:ScheduleOfCapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationTextBlock |
| Documentation: | Tabular disclosure of the capitalized costs of unproved properties and major development projects that are excluded from capitalized costs being amortized. This includes the total costs excluded and, at a minimum, these categories of costs: acquisition costs, exploration costs, development costs in the case of significant development projects, and capitalized interest. |
| 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:ScheduleOfCapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationTextBlock |
| Label | Role | Language |
| Schedule of Capitalized Costs of Unproved Properties Excluded from Amortization [Table Text Block] | http://www.xbrl.org/2003/role/label | en-US |
| Reference | Role | Topic |
| FASB Accounting Standards Codification 932 10 S99 1 (SX 210.4-10(c)(7)(ii)) | http://www.xbrl.org/2003/role/disclosureRef | 932 |