Financial instruments and risk management - Commodity price risk - Additional information (Detail) - Commodity price risk - Copper lb in Millions	12 Months Ended
Dec. 31, 2020 USD ($) lb	Dec. 31, 2019 USD ($) lb
Disclosure of detailed information about financial instruments [line items]
Quantity of unsettled copper sales \| lb	261	220
Provisionally priced unsettled copper sales per pound	$ 336	$ 271
Increase (decrease) in net earnings due to price change	$ 58,000,000	$ 38,000,000
Level 3
Disclosure of detailed information about financial instruments [line items]
Percentage of increase in copper price	10.00%

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]

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 118
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_118_b&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_IncreaseDecreaseThroughCumulativeCatchupAdjustmentsToRevenueArisingFromChangeInEstimateOfTransactionPriceContractAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration