Financial Instruments, Risk Management and Fair Value Measurements - Derivatives in Cash Flow Hedging Relationships (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 540.8	$ 508.6	$ 489.6	$ 544.0	$ 489.6
Unrealized hedging gains, net of tax				(1.8)	1.1
Reclassification of deferred hedging gains, net of tax					(0.7)
Other comprehensive (loss)/income, net of tax	0.0	(0.5)		(1.8)	0.4
Ending balance	571.2	525.3	508.6	571.2	525.3
Total Foreign Exchange Contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0.0	(1.3)	(1.2)	0.0	(1.2)
Unrealized hedging gains, net of tax	(0.2)	0.8	0.3	(0.2)	1.1
Reclassification of deferred hedging gains, net of tax		(0.3)	(0.4)		(0.7)
Other comprehensive (loss)/income, net of tax	(0.2)	0.5	(0.1)
Ending balance	$ (0.2)	$ (0.8)	$ (1.3)	$ (0.2)	$ (0.8)