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Share-based compensation - Weighted average assumptions (Details) - SARs and TSARs	12 Months Ended
	Dec. 31, 2017 USD ($) year	Dec. 31, 2016 USD ($) year
Disclosure of terms and conditions of share-based payment arrangement [line items]
Risk-free interest rate	1.80%	1.00%
Expected dividend yield	2.00%	2.50%
Expected life of SARs and TSARs (years) | year	1.2	1.4
Expected volatility	31.00%	41.00%
Expected forfeitures	0.20%	0.20%
Weighted average fair value (USD per share) | $	$ 19.02	$ 10.19

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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 weighted average fair value at the measurement date of granted equity instruments other than share options. [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 b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_47_b&doctype=Standard
-URIDate 2017-03-09

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Expected Volatility, Other Equity Instruments Granted

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Risk Free Interest Rate, Other Equity Instruments Granted

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