Employees - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Components of net periodic benefit cost:
Service cost	$ 0.2	$ 0.4
Interest cost	1.2	2.4
Expected return on plan assets	(1.8)	(3.6)
Recognition due to settlement	0.0	(0.1)
Net periodic benefit	$ (0.4)	$ (0.9)