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Pensions and Post-Employment Benefits - Summary of Significant Assumptions Used in the Determination of the Benefit Obligation (Detail) - Defined Benefit Obligation [Member] | Dec. 31, 2020 | Dec. 31, 2019
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Mexico [member] |  |
Disclosure of defined benefit plans [line items] |  |
Discount rates | 7.80% | 8.75%
Rate of return on plan assets | 7.80% | 8.75%
Rate of salary increases | 4.50% | 4.00%
United States [member] |  |
Disclosure of defined benefit plans [line items] |  |
Discount rates | 2.60% | 3.60%
Rate of return on plan assets | 2.60% | 3.60%
United Kingdom [member] |  |
Disclosure of defined benefit plans [line items] |  |
Discount rates | 1.50% | 2.10%
Rate of return on plan assets | 1.50% | 2.10%
Rate of salary increases | 3.00% | 3.00%
Top of range [member] | Other countries [member] |  |
Disclosure of defined benefit plans [line items] |  |
Discount rates | 9.00% | 8.80%
Rate of return on plan assets | 9.00% | 8.80%
Rate of salary increases | 6.80% | 6.80%
Bottom of range [member] | Other countries [member] |  |
Disclosure of defined benefit plans [line items] |  |
Discount rates | 0.20% | 0.40%
Rate of return on plan assets | 0.20% | 0.40%
Rate of salary increases | 2.30% | 2.30%

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- Definition 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]] + References 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 + Details
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- Definition 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]] + References 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 + Details
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