Acquisitions and divestitures - Henan Longyu Energy Resources (Details) - Henan Longyu Energy Resources Co., Ltd. $ in Millions	Dec. 27, 2019 USD ($) item
Disclosure of detailed information about business combination [line items]
Percentage of total outstanding common shares disposed	25.00%
Number of coal mines the entity operates \| item	2
Proceeds from sale of assets \| $	$ 152

The cash inflow from the disposal of non-current assets or disposal groups classified as held for sale and discontinued operations. [Refer: Discontinued operations [member]; Disposal groups classified as held for sale [member]; Non-current assets or disposal groups classified as held for sale]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2019-01-01
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2019-en-r&anchor=para_16&doctype=Standard
-URIDate 2019-03-27

Name:	ifrs-full_ProceedsFromDisposalOfNoncurrentAssetsOrDisposalGroupsClassifiedAsHeldForSaleAndDiscontinuedOperations
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration