Employees - Summary of Assumptions for Pension Plans Representing Approximately 84% of Defined Benefit Pension Liability (Detail) - yr	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
United Kingdom [member]
Disclosure of defined benefit plans [Line Items]
Discount rate	2.50%	2.70%
Inflation	3.10%	3.20%
Rate of increase in salaries	3.00%	3.10%
Number of years a current pensioner is expected to live beyond age 65 - Men	22.1	22.5
Number of years a current pensioner is expected to live beyond age 65 - Women	24.0	24.6
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Men	22.6	23.8
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Women	25.6	26.5
United Kingdom [member] \| Pensions in payment [member]
Disclosure of defined benefit plans [Line Items]
Rate of increase for pensions	3.00%	3.10%
United Kingdom [member] \| Pensions in deferment [member]
Disclosure of defined benefit plans [Line Items]
Rate of increase for pensions	3.00%	3.10%
Netherlands [member]
Disclosure of defined benefit plans [Line Items]
Discount rate	1.80%	1.80%
Inflation	1.70%	1.70%
Rate of increase in salaries	2.20%	2.20%
Number of years a current pensioner is expected to live beyond age 65 - Men	22.5	21.8
Number of years a current pensioner is expected to live beyond age 65 - Women	24.3	24.0
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Men	24.6	24.1
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Women	26.6	26.3
Netherlands [member] \| Pensions in payment [member]
Disclosure of defined benefit plans [Line Items]
Rate of increase for pensions	1.70%	1.70%
Netherlands [member] \| Pensions in deferment [member]
Disclosure of defined benefit plans [Line Items]
Rate of increase for pensions	1.70%	1.70%

The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: 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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- Definition

The expected rate of inflation that is 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]]

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- Definition

The expected rate of increases in pension that is 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]]

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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]]

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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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Longevity for current pensioners, females.

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Longevity for current pensioners, males.

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Longevity for future pensioners, females.

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Longevity for future pensioners, males.

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