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Significant Events - Summary of Provision for Samarco Dam Failure (Detail) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Dec. 31, 2019
Jun. 30, 2019
Disclosure of other provisions [line items]    
Current $ 2,106 $ 2,175
Non-current 9,459 8,928
Samarco dam failure [member]    
Disclosure of other provisions [line items]    
At the beginning of the reporting period 1,914 1,285
Movement in provisions (186) 629
Utilised (177)  
Change in estimate 28 579
Amortisation of discounting impacting net finance costs 57 108
Exchange translation (84)  
Current 500 440
Non-current 1,228 1,474
At the end of the reporting period 1,728 1,914
Samarco dam failure [member] | Samarco Total Provision [Member]    
Disclosure of other provisions [line items]    
Utilised (180) (328)
Exchange translation (97) 7
Samarco dam failure [member] | Samarco Germano Dam Decommissioning One [Member]    
Disclosure of other provisions [line items]    
Change in estimate $ 6 $ 263