CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) shares in Millions, $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Beginning Balance at Dec. 31, 2016	$ 2,816.4		$ 0.8	$ 1,166.5	$ 2,006.1	$ (367.6)	$ 10.6
Beginning Balance (in shares) at Dec. 31, 2016		0.7	85.2
Net income	43.0				42.4		0.6
Currency translation adjustment	80.5					79.3	1.2
Change in qualifying cash flow hedge, net of tax	1.3					1.3
Issuance of common stock for exercise of options and employee stock purchases, net	17.3		$ 0.1	17.2
Issuance of common stock for exercise of options and employee stock purchases, net			0.3
Repurchase and cancellation of convertible preferred stock	(34.2)			(51.5)	17.3
Preferred stock dividend	(36.3)				(36.3)
Stock compensation expense	21.3			21.3
Payments to noncontrolling interest	(0.7)			(0.3)			(0.4)
Ending Balance at Dec. 31, 2017	2,908.6		$ 0.9	1,153.2	2,029.5	(287.0)	12.0
Ending Balance (in shares) at Dec. 31, 2017		0.7	85.5
Net income	73.6				73.7		(0.1)
Currency translation adjustment	(56.9)					(56.3)	(0.6)
Change in qualifying cash flow hedge, net of tax	0.8					0.8
Issuance of common stock for exercise of options and employee stock purchases, net	16.9			16.9
Issuance of common stock for exercise of options and employee stock purchases, net			0.4
Repurchase and cancellation of convertible preferred stock	(17.2)			(34.1)	16.9
Repurchase and cancellation of convertible preferred stock (in shares)		(0.1)
Conversion of convertible preferred stock to common stock, (in shares)		(0.6)	4.7
Preferred stock dividend	(25.5)				(25.5)
Stock compensation expense	19.5			19.5
Payments to noncontrolling interest	(0.2)						(0.2)
Cumulative effect of new accounting standard (see Note 1)	13.0				13.0
Ending Balance at Sep. 30, 2018	$ 2,932.6		$ 0.9	$ 1,155.5	$ 2,107.6	$ (342.5)	$ 11.1
Ending Balance (in shares) at Sep. 30, 2018			90.6