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Employees - Summary of Principal Defined Benefit Liabilities and Split of Liabilities Between Different Categories of Plan Participants (Detail) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
United Kingdom [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Duration (years) |  | 18 years | 18 years
Netherlands [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Duration (years) |  | 18 years | 19 years
Rest of The World [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Duration (years) | [1] | 13 years | 13 years
Bottom of range [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Duration (years) |  | 7 years | 7 years
Top of range [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Duration (years) |  | 22 years | 23 years
Active members [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 14.00% | 16.00%
Active members [Member] | United Kingdom [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 12.00% | 14.00%
Active members [Member] | Netherlands [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 12.00% | 14.00%
Active members [Member] | Rest of The World [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities | [1] | 20.00% | 21.00%
Deferred members [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 32.00% | 31.00%
Deferred members [Member] | United Kingdom [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 35.00% | 34.00%
Deferred members [Member] | Netherlands [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 43.00% | 41.00%
Deferred members [Member] | Rest of The World [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities | [1] | 17.00% | 17.00%
Retired members [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 54.00% | 53.00%
Retired members [Member] | United Kingdom [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 53.00% | 52.00%
Retired members [Member] | Netherlands [Member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities |  | 45.00% | 45.00%
Retired members [Member] | Rest of The World [member] |  |  |
Disclosure of defined benefit plans [line items] |  |  |
Percentage of defined benefit liabilities | [1] | 63.00% | 62.00%
[1] | Rest of world numbers shown are weighted averages by liabilities.

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- Definition 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. + References No definition available. + Details
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- Definition Percentage of defined benefit liabilities participants. + References No definition available. + Details
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- Details
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- Details
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