Retirement Benefit Plans - Funded status of plans with ABO in excess of plan assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ (649.9)	$ (681.2)
Plan assets	449.9	494.8
Funded status of plan	(200.0)	(186.4)
Germany
Defined Benefit Plan Disclosure [Line Items]
Funded status of plan	(95.4)	(75.7)
United States
Defined Benefit Plan Disclosure [Line Items]
Funded status of plan	(37.1)	(43.2)
Other
Defined Benefit Plan Disclosure [Line Items]
Funded status of plan	$ (67.5)	$ (67.5)