Goodwill and Intangible Assets (Goodwill and Changes in Carrying Amount of Goodwill by Operating Segment) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Balance December 31, 2017	$ 610.5
Acquisitions of businesses	23.8
Currency translation and other adjustments	1.3
Balance March 31, 2018	635.6
Specialty Engineered Materials
Goodwill [Roll Forward]
Balance December 31, 2017	173.2
Acquisitions of businesses	0.0
Currency translation and other adjustments	0.0
Balance March 31, 2018	173.2
Color, Additives and Inks
Goodwill [Roll Forward]
Balance December 31, 2017	424.5
Acquisitions of businesses	23.8
Currency translation and other adjustments	1.3
Balance March 31, 2018	449.6
Performance Products and Solutions
Goodwill [Roll Forward]
Balance December 31, 2017	11.2
Acquisitions of businesses	0.0
Currency translation and other adjustments	0.0
Balance March 31, 2018	11.2
PolyOne Distribution
Goodwill [Roll Forward]
Balance December 31, 2017	1.6
Acquisitions of businesses	0.0
Currency translation and other adjustments	0.0
Balance March 31, 2018	$ 1.6