Other, Net - Summary of other, net (income) expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Realized Investment Gains (Losses)	$ 1.3	$ 1.7	$ 2.3
Foreign currency exchange transactions	0.9	0.0	(2.3)
Gain on equity investments	(0.3)	(0.2)	(0.2)
Non-service cost component of pension cost	(4.3)	(2.7)	(1.3)
Other	(0.2)	2.2	(3.9)
Other, net	$ (3.9)	$ (0.7)	$ (7.7)