Retirement Benefits - Schedule of Net Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 0.3	$ 0.4	$ 0.7		$ 0.9
Interest cost	0.6	0.5	1.3		1.0
Expected return on plan assets	(0.9)	(0.6)	(2.0)		(1.3)
Amortization of net actuarial losses	0.2	0.1	0.5	[1]	0.3	[1]
Net periodic pension cost	$ 0.2	$ 0.4	$ 0.5		$ 0.9

[1] Reflects amounts reclassified from accumulated other comprehensive income to net income.