Inventory valuation (Details) - Hydrocarbon Inventory [Member] - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Disclosure of financial assets [line items]
Inventory valuation reserve	$ 242	$ 38
Inventory write-down	$ 120	$ (15)

The amount of expense recognised related to the write-down of inventories to net realisable value. [Refer: Inventories]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 2
-IssueDate 2018-01-01
-Paragraph 36
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=2&date=2018-03-01&anchor=para_36_e&doctype=Standard
-URIDate 2018-03-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 98
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_98_a&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_InventoryWritedown2011
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration