Financial instruments and risk management - Additional information (Detail) lb in Millions	12 Months Ended
Dec. 31, 2023 USD ($) lb	Dec. 31, 2022 USD ($) lb
Disclosure of detailed information about financial instruments [line items]
Expected unconditional royalty payments to be received	$ 214,000,000	$ 209,000,000
Percentage of change in coal spot price	15.00%
Forecast
Disclosure of detailed information about financial instruments [line items]
Expected unconditional royalty payments to be received	$ 90,000,000
Level 3
Disclosure of detailed information about financial instruments [line items]
Percentage of change in coal spot price	15.00%
Percentage of change in spot price	15.00%
Increase in carrying value of forward contract due to coal spot price assumptions	$ 64,000,000	68,000,000
Decrease in carrying value of forward contract due to decrease in spot price	39,000,000	18,000,000
Level 3 \| Aluminium embedded derivatives separated from the power contract
Disclosure of detailed information about financial instruments [line items]
Long-term embedded derivatives with fair value	186,000,000	208,000,000
Interest rate risk \| Pound sterling
Disclosure of detailed information about financial instruments [line items]
Increase in financial derivative charges on interest rate before tax	33,000,000	35,000,000
Interest rate risk \| US dollar
Disclosure of detailed information about financial instruments [line items]
Increase in financial derivative charges on interest rate before tax	$ 42,000,000	$ 48,000,000
Interest rate risk \| Floating interest rate
Disclosure of detailed information about financial instruments [line items]
Adjusted borrowings, interest rate	68.00%	77.00%
Interest rate risk \| SOFR
Disclosure of detailed information about financial instruments [line items]
Reasonably possible change in risk variable, percent	1.00%
Borrowing cost recognised	$ 5,000,000	$ 26,000,000
Commodity price risk \| Copper
Disclosure of detailed information about financial instruments [line items]
Quantity of unsettled copper sales \| lb	92	83
Provisionally priced unsettled copper sales per pound	$ 3.87	$ 3.80
Increase (decrease) in net earnings due to price change	$ 22,000,000	$ 19,000,000
Commodity price risk \| Copper \| Level 3
Disclosure of detailed information about financial instruments [line items]
Percentage of increase in copper price	10.00%
Foreign exchange risk
Disclosure of detailed information about financial instruments [line items]
Percentage of change in annual foreign exchange rate	10.00%

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.

No definition available.

+ Details

Name:	ifrs-full_DisclosureOfFinancialInstrumentsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The increase (decrease) in contract assets resulting from cumulative catch-up adjustments to revenue arising from a change in an estimate of the transaction price. The transaction price is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, excluding amounts collected on behalf of third parties (for example, some sales taxes). [Refer: Increase (decrease) through cumulative catch-up adjustments to revenue, contract assets]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 15
-IssueDate 2023-01-01
-Paragraph 118
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2023-en-r&anchor=para_118_b&doctype=Standard
-URIDate 2023-03-23