Loans, borrowings and cash and cash equivalents - Liquidity risk (Details) - Credit facilities maturing in 2020 And 2022 $ in Millions	Dec. 31, 2018 USD ($) facility
Loans and borrowings
Number of credit facilities that mature in 2020 and 2022 \| facility	2
Notional amount \| $	$ 5,000

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_NotionalAmount
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant