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Exceptional Items - Summary of Exceptional Items Related to the Samarco Dam Failure (Detail) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jun. 30, 2018
Expenses excluding net finance costs:      
Costs incurred directly by BHP Billiton Brasil and other BHP entities in relation to the Samarco dam failure $ (13,695) $ (13,697) $ (27,527)
Loss from equity accounted investments, related impairments and expenses:      
Samarco dam failure provision (70) (87) (429)
Net finance costs (533) (658) (1,245)
Loss before taxation (210) (210) (650)
Samarco dam failure [member]      
Expenses excluding net finance costs:      
Costs incurred directly by BHP Billiton Brasil and other BHP entities in relation to the Samarco dam failure (33) (29) (57)
Loss from equity accounted investments, related impairments and expenses:      
Share of loss relating to the Samarco dam failure (47) (50) (80)
Samarco dam failure provision (70) (87) (429)
Net finance costs (60) (44) (84)
Loss before taxation $ (210) $ (210) $ (650)