Pensions and Other Post-employment Benefit Obligations - Summary of Actuarial Assumptions (Detail)	Dec. 31, 2017	Dec. 31, 2016
Switzerland [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	1.50%	1.65%
Discount rate	0.65%	0.60%
United States [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries		3.80%
United States [member] \| Hourly pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	2.20%
United States [member] \| Salaried pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	3.80%
Discount rate	3.80%	4.45%
United States [member] \| Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	3.80%
United States [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	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	1.50%	1.60%
France [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	1.20%	1.30%
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	1.60%	1.65%
Bottom of range [member] \| United States [member] \| Hourly pension [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.70%	4.30%
Bottom of range [member] \| United States [member] \| Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.70%	4.20%
Bottom of range [member] \| United States [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.60%	4.05%
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	3.75%	4.35%
Top of range [member] \| United States [member] \| Other post employment benefit [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.85%	4.60%
Top of range [member] \| United States [member] \| Other benefits [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Discount rate	3.70%	4.20%
Top of range [member] \| France [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Rate of increase in salaries	1.75%	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 2017-01-01
-Paragraph 144
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_144&doctype=Standard
-URIDate 2017-03-09

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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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