| Costs incurred and recognised profits (less recognised losses) | en | http://www.xbrl.org/2003/role/label | http://www.xbrl.org/2003/role/link |
| Concept not required due to removal of IAS 11 | en | http://www.xbrl.org/2009/role/deprecatedLabel | http://www.xbrl.org/2003/role/link |
| 2018-01-01 | en | http://www.xbrl.org/2009/role/deprecatedDateLabel | http://www.xbrl.org/2003/role/link |
| The aggregate amount of costs incurred and recognised profits, less recognised losses, to date on construction contracts in progress. | en | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |