Pension and Postretirement Benefits (Assumptions) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Postretirement Medical Benefits
Weighted average assumptions used to determine Benefit Obligations:
Discount rate	3.48%	3.75%	4.25%
Weighted average assumptions used to determine net pension expense:
Discount rate	3.75%	4.25%	3.75%
Domestic Plan
Weighted average assumptions used to determine Benefit Obligations:
Discount rate	3.63%	4.00%	4.75%
Rate of increase in compensation levels	4.01%	4.00%	4.00%
Weighted average assumptions used to determine net pension expense:
Long-term rate of return on assets	6.00%	6.00%	6.25%
Discount rate	4.00%	4.75%	4.00%
Rate of increase in compensation levels	4.01%	4.00%	4.25%
Foreign Plan
Weighted average assumptions used to determine Benefit Obligations:
Discount rate	2.25%	2.34%	3.13%
Rate of increase in compensation levels	3.25%	3.22%	3.61%
Weighted average assumptions used to determine net pension expense:
Long-term rate of return on assets	3.88%	4.68%	5.03%
Discount rate	2.34%	3.13%	3.40%
Rate of increase in compensation levels	3.22%	3.61%	3.95%