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Costs Incurred Relating to Oil and Gas Property Acquisition, Exploration and Development Activities (Parenthetical) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2018
Costs incurred oil and gas property acquisition exploration and development activities [line items]      
Total costs capitalised during the year $ 1,178 $ 1,275 $ 1,970
Total costs 1,738 1,709 2,520
United States [member]      
Costs incurred oil and gas property acquisition exploration and development activities [line items]      
Total costs 992 987 1,975
Discontinued operations - Onshore US Cash Generating Units [member] | United States [member]      
Costs incurred oil and gas property acquisition exploration and development activities [line items]      
Total costs $ 0 $ 331 $ 1,081