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Financial instruments and risk management - Capital and liquidity risk management - Additional information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of detailed information about financial instruments [line items]      
Net debt of the group $ (3,651,000,000) $ 255,000,000 $ (3,845,000,000)
Loss on early redemption of bonds 0 94,000,000 256,000,000
Aggregate cash outflow before fees   1,900,000,000 $ 2,500,000,000
Borrowings 14,115,000,000 12,752,000,000  
Expected unconditional royalty payments to be received $ 124,000,000 158,000,000  
Percentage of change in spot price (15.00%)    
Level 1 [Member]      
Disclosure of detailed information about financial instruments [line items]      
Borrowings at fair value $ 7,700,000,000 7,500,000,000  
Level 3 [Member]      
Disclosure of detailed information about financial instruments [line items]      
Borrowings $ 4,200,000,000 4,200,000,000  
Decrease in carrying value of forward contract due to long-term metal pricing assumptions   22,000,000  
Increase in carrying value of forward contract due to long-term metal pricing assumptions   14,000,000  
Percentage of change in coal spot price 15.00%    
Increase in carrying value of forward contract due to coal spot price assumptions $ 214,000,000 181,000,000  
Decrease in carrying value of forward contract due to decrease in spot price $ 57,000,000 95,000,000  
Liquidity risk [member]      
Disclosure of detailed information about financial instruments [line items]      
Net debt of the group   $ (300,000,000)  
Net debt to total capital percentage 7.00% (1.00%)  
Description of interest coverage on debt 28 22  
Liquidity risk [member] | Rio Tinto Finance (USA) plc and Rio Tinto Finance (USA) Limited [Member]      
Disclosure of detailed information about financial instruments [line items]      
Loss on early redemption of bonds   $ 51,000,000  
Buy-back of bonds   1,900,000,000  
Aggregate cash outflow before fees   2,000,000,000  
Capital And Liquidity Risk Management [Member]      
Disclosure of detailed information about financial instruments [line items]      
Net debt of the group $ (3,651,000,000) 255,000,000  
Description of rating agencies used Standard & Poor’s and Moody’s investor services    
Bottom of range [member] | Liquidity risk [member]      
Disclosure of detailed information about financial instruments [line items]      
Percentage of underlying earnings 40.00%    
Top of range [member] | Liquidity risk [member]      
Disclosure of detailed information about financial instruments [line items]      
Percentage of underlying earnings 60.00%    
Credit Facility Due November 2022 [Member] | Liquidity risk [member]      
Disclosure of detailed information about financial instruments [line items]      
Borrowing maturity $ 5,600,000,000    
Borrowings 1,900,000,000    
Aluminium embedded derivatives separated from the power contract [Member] | Level 3 [Member]      
Disclosure of detailed information about financial instruments [line items]      
Long-term embedded derivatives with fair value $ 120,000,000 338,000,000  
Aluminium forward contracts [Member] | Bottom of range [member]      
Disclosure of detailed information about financial instruments [line items]      
Fair value of derivative commodity price per metric tonne   2,426  
Aluminium forward contracts [Member] | Top of range [member]      
Disclosure of detailed information about financial instruments [line items]      
Fair value of derivative commodity price per metric tonne   2,507  
I F R S16 [Member] | Capital And Liquidity Risk Management [Member]      
Disclosure of detailed information about financial instruments [line items]      
Net debt of the group   $ (1,200,000,000)