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Ageing of Capitalised Exploratory Well Costs (Detail) $ in Millions | Jun. 30, 2018 USD ($) Project | Jun. 30, 2017 USD ($) Project | Jun. 30, 2016 USD ($) Project | Jun. 30, 2015 USD ($)
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Capitalized Exploratory Well Costs [Abstract] |  |  |  |
Exploratory well costs capitalised for a period of one year or less | $ 124 | $ 120 | $ 262 |
Exploratory well costs capitalised for a period greater than one year | 670 | 548 | 508 |
At the end of the year | $ 794 | $ 668 | $ 770 | $ 484
Number of projects that have been capitalised for a period greater than one year | Project | 17 | 14 | 23 |

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- Definition The amount of capitalized exploratory well costs that is pending the determination of proved reserves. This does not include amounts that were capitalized and subsequently expensed in the same annual period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447 + Details
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- Definition The amount of exploratory well costs that have been capitalized for a period of greater than one year after the completion of drilling. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph b -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447 + Details
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- Definition The amount of exploratory well costs that have been capitalized for a period of one year or less after the completion of drilling. + References No definition available. + Details
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- Definition The number of projects for which exploratory well costs have been capitalized for a period of greater than one year after the completion of drilling. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 1B -Subparagraph b -URI http://asc.fasb.org/extlink&oid=68064819&loc=SL6806780-109447 + Details
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