Interest-bearing loans and borrowings - Undrawn borrowing facilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financial Instruments [Abstract]
Undrawn credit line facilities	$ 753.1	$ 498.9

The amount of undrawn borrowing facilities that may be available for future operating activities and to settle capital commitments. [Refer: Capital commitments]

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2018-01-01
-Paragraph 50
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2018-03-01&anchor=para_50_a&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_UndrawnBorrowingFacilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant