| Gross amount due from customers for contract work as asset | 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 amount recognised as an asset as the net of: (a) costs incurred plus recognised profits; less (b) the sum of recognised losses and progress billings for all contracts in progress for which costs incurred plus recognised profits (less recognised losses) exceeds progress billings. | en | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |