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Discontinued Operations - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Oct. 31, 2018
Sep. 28, 2018
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2019
Disclosure of analysis of single amount of discontinued operations [line items]          
Total comprehensive income (loss) attributable to BHP shareholders     $ (11,352) $ (7,898) $ (8,282)
Discontinued operations [member]          
Disclosure of analysis of single amount of discontinued operations [line items]          
Total comprehensive income (loss) attributable to BHP shareholders         $ 342
BHP Billiton Petroleum (Arkansas) Inc. [member] | Discontinued operations [member]          
Disclosure of analysis of single amount of discontinued operations [line items]          
Percentage of issued share capital sold   100.00%      
BHP Billiton Petroleum (Fayetteville) LLC [member] | Discontinued operations [member]          
Disclosure of analysis of single amount of discontinued operations [line items]          
Percentage of issued share capital sold   100.00%      
BHP Billiton Petroleum Arkansas and BHP Billiton Petroleum Fayetteville LLC [member] | Discontinued operations [member]          
Disclosure of analysis of single amount of discontinued operations [line items]          
Agreement purchase price   $ 300      
Petrohawk Energy Corporation [member] | Discontinued operations [member]          
Disclosure of analysis of single amount of discontinued operations [line items]          
Percentage of issued share capital sold 100.00%        
Agreement purchase price $ 10,300        
Customary completion adjustments $ 200