Income taxes - Deferred tax assets not recognized (Details) $ in Millions	Dec. 31, 2018 USD ($)
Deferred tax assets and liabilities
Undistributed reserves of subsidiaries for which no deferred tax liability is recognized	$ 10,713
Unused tax losses for which no deferred tax asset recognised	3,315
France
Deferred tax assets and liabilities
Unused tax losses for which no deferred tax asset recognised	470
Australia
Deferred tax assets and liabilities
Unused tax losses for which no deferred tax asset recognised	370
Nigeria
Deferred tax assets and liabilities
Unused tax losses for which no deferred tax asset recognised	303
Canada
Deferred tax assets and liabilities
Unused tax losses for which no deferred tax asset recognised	$ 250

The aggregate amount of temporary differences associated with investments in subsidiaries, branches and associates and interests in joint arrangements, for which deferred tax liabilities have not been recognised as a result of satisfying both of the following conditions: (a) the parent, investor, joint venturer or joint operator is able to control the timing of the reversal of the temporary difference; and (b) it is probable that the temporary difference will not reverse in the foreseeable future. [Refer: Associates [member]; Subsidiaries [member]; Temporary differences [member]; Investments in subsidiaries]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2018-01-01
-Paragraph 81
-Subparagraph f
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2018-03-01&anchor=para_81_f&doctype=Standard
-URIDate 2018-03-16

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