Accumulated Other Comprehensive Loss - OCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other comprehensive income, net of tax
Pre-tax amount	$ 10.8	$ (37.7)	$ (140.4)	$ (2.4)
Tax impact	(0.1)	0.4	2.1	1.9
Net amount	10.7	(37.3)	(138.3)	(0.5)
Foreign currency translation adjustments
Other comprehensive income, net of tax
Pre-tax amount	12.1	(37.7)	(139.2)	(2.4)
Tax impact	(0.1)	0.4	2.1	1.9
Net amount	12.0	$ (37.3)	(137.1)	$ (0.5)
Retirement benefit asset, net
Other comprehensive income, net of tax
Pre-tax amount	0.1		0.2
Net amount	0.1		0.2
Reclassification to net income
Other comprehensive income, net of tax
Pre-tax amount	(1.4)		(1.4)
Net amount	$ (1.4)		$ (1.4)