Weighted-Average Assumptions Used to Determine Benefit Obligations (Detail)	Dec. 31, 2017	Dec. 31, 2016
Pension Plans [Member]
Schedule Of Benefit Obligations Weighted Average Assumptions [Line Items]
Discount rate	3.46%	3.89%
Rate of compensation increase	3.71%	3.72%
Other Retirement Plans [Member]
Schedule Of Benefit Obligations Weighted Average Assumptions [Line Items]
Discount rate	3.45%	3.85%