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Pensions and Other Post-employment Benefit Obligations - Summary of Actuarial Assumptions (Detail)
Jun. 30, 2018
Dec. 31, 2017
Switzerland [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 0.80% 0.65%
United States [member] | Salaried pension [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 4.35% 3.80%
France [member] | Retirements [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 1.60% 1.50%
France [member] | Other benefits [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 1.30% 1.20%
Germany [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 1.60% 1.60%
Bottom of range [member] | United States [member] | Hourly pension [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 4.30% 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 4.30% 3.70%
Bottom of range [member] | United States [member] | Other benefits [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 4.20% 3.60%
Top of range [member] | United States [member] | Hourly pension [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 4.35% 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 4.40% 3.85%
Top of range [member] | United States [member] | Other benefits [member]    
Disclosure of sensitivity analysis for actuarial assumptions [line items]    
Discount rate 4.30% 3.70%