Postretirement Benefit Plans - Weighted-Average Assumptions used to Determine Benefit Obligations (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cost Assumptions:
Expected return on plan assets	7.00%	7.20%	8.00%
Other Postretirement Benefits Plan [Member]
Obligation Assumptions:
Discount rate	3.60%	4.10%
Cost Assumptions:
Discount rate	4.10%	4.10%
Expected return on plan assets	7.00%	7.20%
U.S. Plan [Member] | Pension Plan [Member]
Obligation Assumptions:
Discount rate	3.60%	4.20%
Cost Assumptions:
Discount rate	4.20%	4.30%
Expected return on plan assets	7.00%	7.20%
International Plan [Member] | Pension Plan [Member]
Obligation Assumptions:
Discount rate	1.70%	1.70%
Rate of future compensation increase	3.30%	3.40%
Cost Assumptions:
Discount rate	1.70%	2.30%
Expected return on plan assets	1.00%	4.80%