Pensions and Other Post-employment Benefit Obligations - Summary of Actuarial Assumptions (Detail)	Dec. 31, 2018	Dec. 31, 2017
Switzerland [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	1.50%	1.50%
Discount rate	0.80%	0.65%
United States [member] \| Hourly pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	2.20%	2.20%
United States [member] \| Salaried pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	3.80%	3.80%
Discount rate	4.45%	3.80%
United States [member] \| Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	3.80%	3.80%
United States [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	3.80%	3.80%
France [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in pension	2.00%	2.00%
France [member] \| Retirements [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	1.65%	1.50%
France [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	1.35%	1.20%
Germany [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	2.75%	2.75%
Rate of increase in pension	1.70%	1.70%
Discount rate	1.70%	1.60%
Bottom of range [member] \| United States [member] \| Hourly pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	4.40%	3.70%
Bottom of range [member] \| United States [member] \| Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	4.40%	3.70%
Bottom of range [member] \| United States [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	4.25%	3.60%
Bottom of range [member] \| France [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	1.50%	1.50%
Top of range [member] \| United States [member] \| Hourly pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	4.45%	3.75%
Top of range [member] \| United States [member] \| Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	4.55%	3.85%
Top of range [member] \| United States [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	4.40%	3.70%
Top of range [member] \| France [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	2.50%	1.75%

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 2018-01-01
-Paragraph 144
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_144&doctype=Standard
-URIDate 2018-03-16

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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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No definition available.

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