Pension - Components of Net Periodic Benefit Cost (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.5	$ 0.4
Interest cost	2.7	2.7
Expected return on plan assets	(4.2)	(4.3)
Settlement charge	(0.1)	0.0
Amortization of net actuarial losses	1.6	1.3
Net periodic cost	$ 0.7	$ 0.1