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.

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The option life of share options granted.

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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]]

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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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The percentage of an expected dividend used to calculate the fair value of share options granted.

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The weighted average fair value of share options granted during the period at the measurement date. [Refer: Weighted average [member]]

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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]]

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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%