Assumptions Used in Determining Benefit Obligation and Net Periodic Benefit Cost for Pension Plans (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Benefit obligations, Discount rate	0.82%	0.63%	1.10%
Benefit obligations, Rate of compensation increase	3.05%	2.90%	3.70%
Net periodic benefit cost, Discount rate	1.45%	1.70%	1.94%
Net periodic benefit cost, Rate of compensation increase	3.00%	3.43%	4.41%
Net periodic benefit cost, Expected return on plan assets	1.80%	1.43%	1.76%