Retirement Plans and Postretirement Medical Benefits (Weighted-Average Actuarial Assumptions) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	6.25%	6.50%
United States
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.69%	4.20%	4.55%
Discount rate	4.20%	4.55%	4.15%
Expected return on plan assets	6.75%	7.00%	7.00%
Foreign | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	0.65%	0.70%	1.15%
Discount rate	0.70%	1.15%	1.10%
Expected return on plan assets	3.75%	3.75%	4.00%
Rate of compensation increase	1.50%	1.50%	1.50%
Rate of compensation increase	1.50%	1.50%	1.50%
Foreign | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.35%	3.65%	3.95%
Discount rate	3.65%	3.95%	3.80%
Expected return on plan assets	6.25%	6.51%	7.00%
Rate of compensation increase	2.50%	2.50%	3.50%
Rate of compensation increase	3.30%	3.50%	3.50%
Pension Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.55%	3.90%	4.20%
Discount rate	3.90%	4.20%	3.90%
Pension Benefits | Canada
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.35%	3.65%	3.95%
Discount rate	3.65%	3.95%	3.80%