Receivables and other assets - Summary of trade and other receivables (Parenthetical) (Detail) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Trade and other receivables [abstract]
Net of provisions for doubtful debts	$ (59,000,000)	$ (54,000,000)
Amount held in trust fund, noncurrent	315,000,000	53,000,000
Amount held in trust fund, current	95,000,000	$ 0
Deposits into trust fund	$ (299,000,000)

The amount of an allowance account used to record impairments to financial assets due to credit losses. [Refer: Financial assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2021-01-01
-Name IFRS
-Number 7
-IssueDate 2020-01-01
-Paragraph 16
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2017-en-b&anchor=para_16&doctype=Standard&book=b
-URIDate 2020-01-01

Name:	ifrs-full_AllowanceAccountForCreditLossesOfFinancialAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant