Derivative financial instruments - Carrying and notional amounts of hedges (Details) - Cash flow hedges $ in Millions	Dec. 31, 2021 USD ($) MMBTU	Dec. 31, 2020 USD ($) MMBTU
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	$ 1	$ 4
Hedging instrument, liabilities	0	0
Highly probable forecast capital expenditure \| Foreign exchange risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	1	4
Hedging instrument, liabilities	0	0
Nominal amounts of hedging instruments	55	162
Highly probable forecast sales \| Commodity price risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0	0
Hedging instrument, liabilities	$ 0	$ 0
Nominal Amounts Of Hedging Instruments \| MMBTU	(420,000,000)	(175,000,000)

Nominal Amounts Of Hedging Instruments

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- Definition

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+ References

No definition available.

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- Definition

The amount of a hedging instrument, recognised as an asset. [Refer: Hedging instruments [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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-IssueDate 2021-01-01
-Paragraph 24A
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- Definition

The amount of a hedging instrument, recognised as a liability. [Refer: Hedging instruments [member]]

+ References

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- Definition

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
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-IssueDate 2021-01-01
-Paragraph 112
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