Retirement and Deferred Compensation Plans - Weighted-Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
United States Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Rate of compensation increase	3.00%	3.00%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Rate of compensation increase	3.00%	3.00%	3.00%
Non-United States Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Rate of compensation increase	1.80%	1.90%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Rate of compensation increase	1.80%	1.70%	2.20%
Pension plans | United States Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	4.20%	3.60%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate - service cost	3.60%	4.10%	4.40%
Discount rate - interest cost	3.20%	3.30%	3.40%
Expected long-term return on plan assets	4.50%	4.80%	5.30%
Pension plans | Non-United States Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	2.40%	2.10%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate - service cost	2.10%	2.20%	3.20%
Discount rate - interest cost	2.10%	2.20%	3.20%
Expected long-term return on plan assets	2.70%	2.80%	3.40%