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Movement in Capitalised Exploratory Well Costs (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2017
Extractive Industries [Abstract] |  |  |
At the beginning of the year | $ 794 | $ 668 | $ 770
Additions to capitalised exploratory well costs pending the determination of proved reserves | 297 | 186 | 258
Capitalised exploratory well costs charged to expense | (9) | (62) | (69)
Capitalised exploratory well costs reclassified to wells, equipment, and facilities based on the determination of proved reserves | (42) | 2 | (155)
Other |  |  | (136)
At the end of the year | $ 1,040 | $ 794 | $ 668

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- Definition Capitalized exploratory well cost charged to expense. + References No definition available. + Details
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Namespace Prefix: | bhp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Capitalized exploratory well cost. + References No definition available. + Details
Name: | bhp_CapitalizedExploratoryWellCosts
Namespace Prefix: | bhp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Capitalized exploratory well costs, additions pending determination of proved reserves. + References No definition available. + Details
Name: | bhp_CapitalizedExploratoryWellCostsAdditionsPendingDeterminationOfProvedReserves
Namespace Prefix: | bhp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of other changes in capitalized exploratory well costs. + References No definition available. + Details
Name: | bhp_CapitalizedExploratoryWellCostsOther
Namespace Prefix: | bhp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Reclassification to wells, facilities, and equipment based on determination of proved reserves. + References No definition available. + Details
Name: | bhp_ReclassificationToWellsFacilitiesAndEquipmentBasedOnDeterminationOfProvedReserves
Namespace Prefix: | bhp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | srt_ExtractiveIndustriesAbstract
Namespace Prefix: | srt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration