Long-Term Employee Benefit Liabilities - Summary of Weighted Average Discount Rates Used in Measuring Company's Projected Retirement Medical Benefit Obligations and Net Periodic Benefit Cost (Detail) - Retirement Medical Benefits Plans [Member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Retirement medical benefit obligations	4.00%	3.40%
Net periodic benefit cost	3.40%	3.80%
Health care cost inflation	6.80%	6.60%