Derivative financial instruments - Weighted average exchange rates and sales prices, cash flow hedges (Details) - Cash flow hedges	12 Months Ended
Dec. 31, 2021 MMBTU gBPPerUSD	Dec. 31, 2021 MMBTU kRWPerUSD	Dec. 31, 2020 gBPPerUSD	Dec. 31, 2020 kRWPerUSD
Highly probable forecast capital expenditure
Disclosure of detailed information about hedges [line items]
Average foreign exchange rate (per USD)	1.33	0	1.35	1,174.47
Highly probable forecast sales
Disclosure of detailed information about hedges [line items]
Average price of hedging instrument (Henry Hub $/mmBtu)	3.24	3.24	2.88	2.88

The average exchange rate used by the entity. Exchange rate is the ratio of exchange for two currencies.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

The average price of a hedging instrument. [Refer: Hedging instruments [member]]

+ References

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

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

+ References

No definition available.

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