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Employees - Summary of Employees (Parenthetical) (Detail) | 12 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2016
Disclosure Of Average Number Of Employees [Abstract] |  |  |
Percentage of employees of subsidiary companies | 100.00% | 100.00% | 100.00%

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- Definition Disclosure of average number of employees. + References No definition available. + Details
Name: | bhp_DisclosureOfAverageNumberOfEmployeesAbstract
Namespace Prefix: | bhp_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of employees of subsidiary companies included in the the Group employee number. + References No definition available. + Details
Name: | bhp_PercentageOfEmployeesOfSubsidiaryCompanies
Namespace Prefix: | bhp_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration