| Gross amount due to customers for contract work as liability | 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 a liability 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 progress billings exceed costs incurred plus recognised profits (less recognised losses). | en | http://www.xbrl.org/2003/role/documentation | http://www.xbrl.org/2003/role/link |