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Changes in the Standardised Measure (Detail) - USD ($)
$ in Millions
 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2016
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]      
Standardised measure at the beginning of the year $ 8,242 $ 8,987 $ 17,244
Revisions:      
Prices, net of production costs 5,540 (96) (14,146)
Changes in future development costs (358) 275 1,342
Revisions of quantity estimates (166) 2,961 (2,870)
Accretion of discount 1,016 1,147 2,547
Changes in production timing and other 946 (1,611) 1,280
Revisions 15,220 11,663 5,397
Sales of oil and gas, net of production costs (5,091) (4,301) (3,936)
Acquisitions of reserves-in-place 0 0 0
Sales of reserves-in-place (26) (15) (114)
Previously estimated development costs incurred 1,068 718 1,823
Extensions, discoveries, and improved recoveries, net of future costs 502 (401) 84
Changes in future income taxes (1,433) 578 5,733
Standardised measure at the end of the year $ 10,240 $ 8,242 $ 8,987