Reorganization and Restructuring (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) position	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Reorganization and Restructuring 2016
Restructuring Cost and Reserve [Line Items]
Cumulative costs	$ 46.7
Positions eliminated across the global workforce | position	800
Restructuring Reserve [Roll Forward]
Restructuring Reserve, beginning balance	$ 2.0	$ 7.6	$ 7.6
Expense (benefit)	11.3	13.5	17.3	$ 18.1
Payments and utilization	(12.4)	(17.9)
Foreign currency exchange effects	0.0	0.2
Restructuring Reserve, ending balance	0.9	3.4	2.0	7.6
Asset Related Adjustments | Reorganization and Restructuring 2016
Restructuring Reserve [Roll Forward]
Restructuring Reserve, beginning balance	0.0	0.0	0.0
Expense (benefit)	1.7	3.4
Payments and utilization	(1.7)	(3.4)
Foreign currency exchange effects	0.0
Restructuring Reserve, ending balance	0.0	0.0	0.0	0.0
Severance Costs | Reorganization and Restructuring 2016
Restructuring Reserve [Roll Forward]
Restructuring Reserve, beginning balance	1.6	7.0	7.0
Expense (benefit)	9.6	7.5
Payments and utilization	(10.5)	(11.9)
Foreign currency exchange effects	0.0	0.2
Restructuring Reserve, ending balance	0.7	2.8	1.6	7.0
Severance Costs | Other Restructuring
Restructuring Reserve [Roll Forward]
Expense (benefit)	4.2
Lease Terminations | Reorganization and Restructuring 2016
Restructuring Reserve [Roll Forward]
Restructuring Reserve, beginning balance	0.4	0.6	0.6
Expense (benefit)	0.0	0.4
Payments and utilization	(0.2)	(0.4)
Foreign currency exchange effects	0.0
Restructuring Reserve, ending balance	0.2	0.6	0.4	0.6
Benefit Program Termination | Reorganization and Restructuring 2016
Restructuring Reserve [Roll Forward]
Restructuring Reserve, beginning balance	0.0	0.0	0.0
Expense (benefit)	0.0	2.2
Payments and utilization	0.0	(2.2)
Foreign currency exchange effects	0.0
Restructuring Reserve, ending balance	0.0	$ 0.0	$ 0.0	$ 0.0
Minimum | Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected costs	2.0
Maximum | Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected costs	$ 4.0