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Operating segments - Additional information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of operating segments [Line Items]      
Description of factors used to identify entity's reportable segments Rio Tinto’s management structure is based on the principal product groups in the tables below together with the global functions that support the business, which include Growth & Innovation.    
Description of types of products and services from which each reportable segment derives its revenues Generally, business units are allocated to product groups based on their primary product. The Energy & Minerals product group includes businesses with products such as uranium, borates, salt and titanium dioxide feedstock together with coal operations, Iron Ore Company of Canada and the Simandou iron ore project, which is the responsibility of the Energy & Minerals product group chief executive. The Copper & Diamonds product group also produces gold, silver, molybdenum and other by-products.    
Underlying profits of equity accounted units $ 339 $ 321 $ 361
Subsidiaries [Member]      
Disclosure of operating segments [Line Items]      
Share of sales revenue of equity accounted units $ 22 30 32
Percentage of capital expenditure 100.00%    
Percentage of depreciation and amortisation 100.00%    
Gross sales revenue [Member]      
Disclosure of operating segments [Line Items]      
Share of sales revenue of equity accounted units $ 1,859 1,585 1,987
Underlying earnings [member]      
Disclosure of operating segments [Line Items]      
Underlying profits of equity accounted units 332 309 390
Underlying earnings [member] | Copper & Diamonds [member]      
Disclosure of operating segments [Line Items]      
Underlying profits of equity accounted units 295 272 307
Underlying earnings [member] | Other operations [Member]      
Disclosure of operating segments [Line Items]      
Underlying profits of equity accounted units $ 37 $ 37 $ 83