Retirement Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined contribution expense	$ 34.9	$ 33.5	$ 28.3
Defined benefit pension expense	8.5	12.5	10.1
Other postretirement employee benefit expense	0.1	0.5	1.4
Total	$ 43.5	$ 46.5	$ 39.8