Employees - Summary of Assumptions for Pension Plans Representing Approximately 00% of Defined Benefit Pension Liability (Detail) - yr	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
United Kingdom [Member]
Disclosure of defined benefit plans [line items]
Discount rate	1.40%	2.00%
Inflation	2.70%	2.90%
Rate of increase in salaries	3.30%	3.20%
Number of years a current pensioner is expected to live beyond age 65 - Men	21.7	21.6
Number of years a current pensioner is expected to live beyond age 65 - Women	23.4	23.4
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Men	22.7	22.6
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Women	24.6	24.6
United Kingdom [Member] \| Pensions in payment [Member]
Disclosure of defined benefit plans [line items]
Rate of increase for pensions in payment (where provided)	2.70%	2.80%
United Kingdom [Member] \| Pensions in deferment [Member]
Disclosure of defined benefit plans [line items]
Rate of increase for pensions in deferment (where provided)	2.70%	2.80%
Netherlands [Member]
Disclosure of defined benefit plans [line items]
Discount rate	0.70%	1.10%
Inflation	1.50%	1.50%
Rate of increase in salaries	2.00%	2.00%
Number of years a current pensioner is expected to live beyond age 65 - Men	21.5	22.6
Number of years a current pensioner is expected to live beyond age 65 - Women	23.6	24.1
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Men	23.4	24.5
Number of years a future pensioner currently aged 45 is expected to live beyond age 65 - Women	25.4	26.2
Netherlands [Member] \| Pensions in payment [Member]
Disclosure of defined benefit plans [line items]
Rate of increase for pensions in payment (where provided)	1.50%	1.50%
Netherlands [Member] \| Pensions in deferment [Member]
Disclosure of defined benefit plans [line items]
Rate of increase for pensions in deferment (where provided)	1.50%	1.50%

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 2020-01-01
-Paragraph 144
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_144&doctype=Standard
-URIDate 2020-01-01

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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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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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Actuarial assumption of increase for pensions in deferment where provided

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Actuarial assumption of increase for pensions in payment where provided.

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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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