Employee Benefit Obligations - Summary of Assumptions Used in Actuarial Calculation of Defined Benefits (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure For Actuarial Assumptions [Abstract]
Discount rates used	5.00%	4.70%	4.95%
Expected rate of salary increases	4.00%	4.00%	4.00%
Mortality tables	CB-H-2014 y RV-M-2014	CB-H-2014 and RV-M-2014	RV 2009
Expected rotation rate	3.80%	4.70%	7.00%

The expected rate of salary increases used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2016-01-13
-Paragraph 144
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2016-03-30&anchor=para_144&doctype=Standard
-URIDate 2016-03-31

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