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Employee Share Ownership Plans - Summary of Fair Value and Assumptions in the Calculation of Fair Value for Awards Issued (Detail) | 12 Months Ended |
--- | --- | ---
Jun. 30, 2018 AUD ($) yr | Jun. 30, 2018 GBP (£) yr | Jun. 30, 2018 USD ($)
BHP Billiton Limited [Member] | STIP awards [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | $ 20.65
Estimated life of awards | yr | 3 | 3 |
Share price at grant date | $ 27.97 |  |
BHP Billiton Limited [Member] | GSTIP awards [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | 18.83
Estimated life of awards | yr | 3 | 3 |
Share price at grant date | $ 25.98 |  |
Dividend yield | 4.30% | 4.30% |
BHP Billiton Limited [Member] | Long-Term Incentive Plan [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | 13.11
Risk-free interest rate | 2.08% | 2.08% |
Estimated life of awards | yr | 5 | 5 |
Share price at grant date | $ 27.97 |  |
Estimated volatility of share price | 33.00% | 33.00% |
BHP Billiton Limited [Member] | MAP awards [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | 18.37
Share price at grant date | $ 25.98 |  |
Dividend yield | 4.30% | 4.30% |
BHP Billiton Limited [Member] | MAP awards [member] | Bottom of range [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Estimated life of awards | yr | 1 | 1 |
BHP Billiton Limited [Member] | MAP awards [member] | Weighted average [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Estimated life of awards | yr | 2 | 2 |
BHP Billiton Limited [Member] | MAP awards [member] | Top of range [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Estimated life of awards | yr | 3 | 3 |
BHP Billiton Limited [Member] | Shareplus [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | 18.12
Risk-free interest rate | 1.85% | 1.85% |
Estimated life of awards | yr | 3 | 3 |
Share price at grant date | $ 24.00 |  |
Dividend yield | 4.33% | 4.33% |
BHP Billiton Plc [Member] | GSTIP awards [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | 16.48
Estimated life of awards | yr | 3 | 3 |
Share price at grant date | £ |  | £ 13.29 |
Dividend yield | 5.10% | 5.10% |
BHP Billiton Plc [Member] | MAP awards [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | 15.62
Share price at grant date | £ |  | £ 13.29 |
Dividend yield | 5.10% | 5.10% |
BHP Billiton Plc [Member] | MAP awards [member] | Bottom of range [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Estimated life of awards | yr | 1 | 1 |
BHP Billiton Plc [Member] | MAP awards [member] | Weighted average [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Estimated life of awards | yr | 2 | 2 |
BHP Billiton Plc [Member] | MAP awards [member] | Top of range [Member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Estimated life of awards | yr | 3 | 3 |
BHP Billiton Plc [Member] | Shareplus [member] |  |  |
Disclosure of terms and conditions of share-based payment arrangement [Line Items] |  |  |
Weighted average fair value of awards granted during the year |  |  | $ 13.48
Risk-free interest rate | 0.17% | 0.17% |
Estimated life of awards | yr | 3 | 3 |
Share price at grant date | £ |  | £ 12.34 |
Dividend yield | 5.10% | 5.10% |

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- Definition The expected volatility of the share price used to calculate the fair value of the share options granted. Expected volatility is a measure of the amount by which a price is expected to fluctuate during a period. The measure of volatility used in option pricing models is the annualised standard deviation of the continuously compounded rates of return on the share over a period of time. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 47 -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_a_i&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The option life of share options granted. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 47 -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_a_i&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The implied yield currently available on zero-coupon government issues of the country in whose currency the exercise price for share options granted is expressed, with a remaining term equal to the expected term of the option being valued (based on the option's remaining contractual life and taking into account the effects of expected early exercise). [Refer: Government [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 47 -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_a_i&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The weighted average fair value of share options granted during the period at the measurement date. [Refer: Weighted average [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 47 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_a&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The weighted average share price used as input to the option pricing model to calculate the fair value of share options granted. [Refer: Option pricing model [member]; Weighted average [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2017-01-01 -Paragraph 47 -Subparagraph a -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_a_i&doctype=Standard -URIDate 2017-03-09 + Details
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