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Dividends - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
 6 Months Ended 12 Months Ended
Feb. 19, 2019
Dec. 17, 2018
Dec. 31, 2018
Dec. 31, 2017
Jun. 30, 2018
Disclosure of dividends [line items]          
Dividend per share, after period-end       $ 0.55 $ 0.63
Dividend amount, after period-end       $ 2,928 $ 3,354
Shares in BHP Group Limited that were held by BHP Group Plc     0
Tax rate     30.00% 30.00% 30.00%
Special dividend [member]          
Disclosure of dividends [line items]          
Dividend per share, after period-end   $ 1.02      
Dividend amount, after period-end   $ 5,200      
Major ordinary share transactions [member]          
Disclosure of dividends [line items]          
Dividend per share, after period-end $ 0.55        
Dividend amount, after period-end $ 2,781        
BHP Billiton Limited [member]          
Disclosure of dividends [line items]          
Ordinary shares on issue and held by the public     2,945,000,000    
Number of ordinary shares represented by each American Depositary Share     2    
Tax rate     30.00%    
BHP Billiton Plc [member]          
Disclosure of dividends [line items]          
Ordinary shares on issue and held by the public     2,112,000,000    
Number of ordinary shares represented by each American Depositary Share     2