Related party disclosures - Summary of Related Party Disclosures for Associates and Joint Ventures (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of transactions between related parties [Line Items]
Revenue from associates and joint ventures	$ 9	$ 6	$ 3
Loans to associates		9	7
Other amounts owed by associates and joint ventures	2	1	2
Associates [member]
Disclosure of transactions between related parties [Line Items]
Revenue from associates and joint ventures	8	5	3
Loans to associates		9	7
Other amounts owed by associates and joint ventures	2	1	$ 2
Joint ventures [member]
Disclosure of transactions between related parties [Line Items]
Revenue from associates and joint ventures	$ 1	$ 1

The amounts receivable resulting from related party transactions. [Refer: Related parties [member]]

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- Definition

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

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No definition available.

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The amount of revenue arising from the rendering of services in related party transactions. [Refer: Revenue; Related parties [member]]

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The amount of receivables due from related parties. [Refer: Related parties [member]]

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