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Exceptional Items - Summary of Exceptional Items by Category (Detail) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Jun. 30, 2018
Disclosure of exceptional items [line items]      
Exceptional items gross $ (210) $ (210) $ (650)
Exceptional items tax 242 (2,320) (2,320)
Exceptional items net 32 (2,530) (2,970)
Samarco dam failure [member]      
Disclosure of exceptional items [line items]      
Exceptional items gross (210) (210) (650)
Exceptional items tax
Exceptional items net (210) (210) (650)
US tax reform [member]      
Disclosure of exceptional items [line items]      
Exceptional items tax   (2,320) (2,320)
Exceptional items net   (2,320) (2,320)
Non-controlling interests [member]      
Disclosure of exceptional items [line items]      
Exceptional items gross    
Exceptional items tax    
Exceptional items net    
Attributable to BHP shareholders [member]      
Disclosure of exceptional items [line items]      
Exceptional items gross (210) (210) (650)
Exceptional items tax 242 (2,320) (2,320)
Exceptional items net 32 $ (2,530) $ (2,970)
Global taxation matters [Member]      
Disclosure of exceptional items [line items]      
Exceptional items gross    
Exceptional items tax 242    
Exceptional items net $ 242