Issued share capital - Summary of Issued Share Capital (Detail) - Ordinary shares [member] - shares shares in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Disclosure of classes of share capital [line items]
Issued capital, Beginning balance	1,332.5	1,331.9	1,331.9
Exercise of share options	0.1	0.4	0.6
Issued capital, Ending balance	1,332.6	1,332.3	1,332.5

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.

No definition available.

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- Definition

The number of share options exercised in a share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2017-01-01
-Paragraph 45
-Subparagraph b
-Clause iv
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45_b_iv&doctype=Standard
-URIDate 2017-03-09

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- Definition

The number of shares issued by the entity, for which full payment has been received.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 79
-Subparagraph a
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_79_a_ii&doctype=Standard
-URIDate 2017-03-09

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