Related party transactions - Summary of compensation of key management personnel (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party [Abstract]
Short-term employee benefits	$ 39	$ 64	$ 52
Other long-term employee benefits	5	8	6
Share-based payments	20	27	$ 34
Total	$ 64	$ 99

Related Party [Abstract]

No definition available.

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- Definition

The amount of compensation to key management personnel. [Refer: Key management personnel of entity or parent [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2020-01-01
-Paragraph 17
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-URIDate 2020-01-01

+ Details

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- Definition

The amount of compensation to key management personnel in the form of other long-term employee benefits. [Refer: Other long-term employee benefits; Key management personnel of entity or parent [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2020-01-01
-Paragraph 17
-Subparagraph c
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-URIDate 2020-01-01

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- Definition

The amount of compensation to key management personnel in the form of share-based payments. [Refer: Key management personnel of entity or parent [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2020-01-01
-Paragraph 17
-Subparagraph e
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-URIDate 2020-01-01

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- Definition

The amount of compensation to key management personnel in the form of short-term employee benefits. [Refer: Key management personnel of entity or parent [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 24
-IssueDate 2020-01-01
-Paragraph 17
-Subparagraph a
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-URIDate 2020-01-01

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