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Standardised Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves (Standardised Measure) (Parenthetical) (Detail) - USD ($) $ in Millions | Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2017
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Discounted future net cash flows relating to proved oil and gas reserves [line items] |  |  |  |
Standardised measure | $ 5,058 | $ 9,152 | $ 10,240 | $ 8,242
United States [member] |  |  |  |
Discounted future net cash flows relating to proved oil and gas reserves [line items] |  |  |  |
Standardised measure | 2,346 | 3,590 | 5,257 |
Discontinued operations - Onshore US Cash Generating Units [member] | United States [member] |  |  |  |
Discounted future net cash flows relating to proved oil and gas reserves [line items] |  |  |  |
Standardised measure | $ 0 | $ 0 | $ 1,932 |

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of discounted future accumulated cash inflow relating to proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Form 20-F -Section Item 18 -Subsection Instruction 2 + Details
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