Principal joint operations - Summary of principle joint operations (Detail)	12 Months Ended
Dec. 31, 2018
Tomago Aluminium Joint Venture [member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	Tomago Aluminium Joint Venture
Country of incorporation, Joint Operation	Australia
Principal activities, Joint Operation	Aluminium smelting
Group interest (%), Joint Operation	51.60%
Gladstone Power Station [member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	Gladstone Power Station
Country of incorporation, Joint Operation	Australia
Principal activities, Joint Operation	Power generation
Group interest (%), Joint Operation	42.10%
Hope Downs Joint Venture [member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	Hope Downs Joint Venture
Country of incorporation, Joint Operation	Australia
Principal activities, Joint Operation	Iron ore mining
Group interest (%), Joint Operation	50.00%
Queensland Alumina Limited [member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	Queensland Alumina Limited
Country of incorporation, Joint Operation	Australia
Principal activities, Joint Operation	Alumina production
Group interest (%), Joint Operation	80.00%
Pilbara Iron arrangement [Member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	Pilbara Iron arrangement
Country of incorporation, Joint Operation	Australia
Principal activities, Joint Operation	Infrastructure, corporate and mining services
New Zealand Aluminium Smelters Limited [member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	New Zealand Aluminium Smelters Limited
Country of incorporation, Joint Operation	New Zealand
Principal activities, Joint Operation	Aluminium smelting
Group interest (%), Joint Operation	79.36%
Aluminerie Alouette Inc. [member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	Aluminerie Alouette Inc.
Country of incorporation, Joint Operation	Canada
Principal activities, Joint Operation	Aluminium production
Group interest (%), Joint Operation	40.00%
Pechiney Reynolds Quebec Inc [member]
Disclosure Of Joint Operations [Line Items]
Company of operation, Joint Operation	Pechiney Reynolds Quebec Inc
Country of incorporation, Joint Operation	United States of America
Principal activities, Joint Operation	Aluminium smelting
Group interest (%), Joint Operation	50.20%

The country in which a joint operation of the entity is incorporated. [Refer: Joint operations [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2017-01-01
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-URIDate 2017-03-09

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- Definition

The description of the nature of the entity's relationship with a joint operation (for example, describing the nature of the activities of the joint operation and whether they are strategic to the entity's activities). [Refer: Joint operations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2017-01-01
-Paragraph 21
-Subparagraph a
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_21_a_ii&doctype=Standard
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- Definition

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.

+ References

No definition available.

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- Definition

The name of a joint operation. [Refer: Joint operations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2017-01-01
-Paragraph 21
-Subparagraph a
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_21_a_i&doctype=Standard
-URIDate 2017-03-09

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- Definition

The proportion of ownership interest in a joint operation attributable to the entity. [Refer: Joint operations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Number 12
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-URIDate 2017-03-09

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