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Pensions and Other Post-employment Benefit Obligations - Summary of Actuarial Assumptions (Detail) | Jun. 30, 2018 | Dec. 31, 2017
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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%

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