Post-employment benefits for associates - Sensitivity analysis (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)
Discount rate [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	$ (42)
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	$ 46
Life expectancy [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Duration of reasonably possible increase in actuarial assumption	1 year
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	$ 31
Rate of pension increase [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	$ 15
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	$ (7)
Interest on savings account [Member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	$ 4
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	$ (3)
Rate of salary increase [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.25%
Percentage of reasonably possible decrease in actuarial assumption	0.25%
Increase (decrease) in defined benefit obligation due to increase in actuarial assumption	$ 6
Increase (decrease) in defined benefit obligation due to decrease in actuarial assumption	$ (4)

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by a decrease in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2020-01-01
-Paragraph 145
-Subparagraph a
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-URIDate 2020-01-01

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- Definition

The increase (decrease) in a defined benefit obligation that would have been caused by an increase in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]]

+ References

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- Definition

The reasonably possible percentage of the decrease in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]]

+ References

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- Definition

The reasonably possible percentage of the increase in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]]

+ References

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