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Significant Events - Additional Information (Detail)
R$ in Millions
 6 Months Ended 12 Months Ended
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Jun. 30, 2018
USD ($)
Dec. 31, 2018
BRL (R$)
Dec. 31, 2018
USD ($)
Aug. 08, 2018
BRL (R$)
Aug. 08, 2018
USD ($)
Jun. 30, 2017
USD ($)
Samarco dam failure [member]                
Disclosure of significant events [line items]                
Funding provided during the period $ 47,000,000              
Additional share of losses 47,000,000 $ 50,000,000 $ 80,000,000          
Provision before tax and after discounting in respect of its obligations under the Framework Agreement     1,285,000,000   $ 1,247,000,000     $ 1,057,000,000
Utilisation of the Samarco dam failure provision 168,000,000   $ 285,000,000          
Samarco dam failure [member] | Dam Stabilisation and Expert Costs [member]                
Disclosure of significant events [line items]                
Utilisation of the Samarco dam failure provision $ 4,000,000              
Samarco dam failure [member] | Framework agreement [member]                
Disclosure of significant events [line items]                
Term of agreement 15 years              
Samarco dam failure [member] | Governance Agreement [member] | Federal public prosecution office claim [member]                
Disclosure of significant events [line items]                
Settlement claim           R$ 155,000 $ 40,000,000,000  
Samarco dam failure [member] | Preliminary Agreement [member] | Federal public prosecution office claim [member]                
Disclosure of significant events [line items]                
Preliminary agreement suspended amount       R$ 7,700 2,000,000,000      
Samarco Mineracao S.A. [member]                
Disclosure of significant events [line items]                
Percentage of interest in joint venture investment 50.00% 50.00% 50.00%          
BHP Billiton Brasil Ltda [member] | Samarco dam failure [member] | Framework agreement [member]                
Disclosure of significant events [line items]                
Provision before tax and after discounting in respect of its obligations under the Framework Agreement     $ 1,300,000,000   1,200,000,000      
Percentage of remaining costs expected to be incurred by December 2020 55.00%              
BHP Billiton Brasil Ltda [member] | Samarco dam failure [member] | Governance Agreement [member]                
Disclosure of significant events [line items]                
Term of agreement 30 months              
Interim security amount preliminary agreement       2,200 570,000,000      
BHP Billiton Brasil Ltda [member] | Samarco dam failure [member] | Governance Agreement [member] | Insurance bonds [Member]                
Disclosure of significant events [line items]                
Interim security amount preliminary agreement       1,300 335,000,000      
BHP Billiton Brasil Ltda [member] | Samarco dam failure [member] | Governance Agreement [member] | Liquid assets [Member]                
Disclosure of significant events [line items]                
Interim security amount preliminary agreement       100 25,000,000      
BHP Billiton Brasil Ltda [member] | Samarco dam failure [member] | Governance Agreement [member] | Charge over assets [member]                
Disclosure of significant events [line items]                
Interim security amount preliminary agreement       R$ 800 205,000,000      
BHP Billiton Brasil Ltda [member] | Samarco Mineracao S.A. [member]                
Disclosure of significant events [line items]                
Adjustment in joint venture investment     0          
Funding provided during the period     47,000,000          
Additional share of losses     47,000,000          
Dividends received     0          
Profits available for distribution     $ 0          
Percentage of interest in joint venture investment 50.00%              
BHP Billiton Brasil Ltda [member] | Samarco Mineracao S.A. [member] | Samarco dam failure [member]                
Disclosure of significant events [line items]                
Undrawn amount $ 2,000,000              
BHP Billiton Brasil Ltda [member] | Samarco Mineracao S.A. [member] | Samarco dam failure [member] | Dam Stabilisation and Expert Costs [member]                
Disclosure of significant events [line items]                
Utilisation of the Samarco dam failure provision $ 4,000,000              
BHP Billiton Brasil Ltda [member] | Samarco Mineracao S.A. [member] | Samarco dam failure [member] | Short-term facility [Member]                
Disclosure of significant events [line items]                
Commitments         $ 77,000,000