Post-Employment Plans - Net periodic pension cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	$ 2.9	$ 3.3	$ 3.9
Interest cost	5.2	2.7	2.6
Expected return on assets	(5.8)	(4.9)	(5.5)
Settlement	(0.1)	0.1	1.1
Curtailment	(0.3)	0.0	0.0
Net actuarial loss/(gain)	(0.5)	0.1	0.1
Net periodic pension cost/(gain)	1.4	1.3	2.2
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs	0.0	0.0	0.0
Interest cost	0.1	0.1	0.1
Expected return on assets	0.0	0.0	0.0
Settlement	0.0	0.0	0.0
Curtailment	0.0	0.0	0.0
Net actuarial loss/(gain)	(1.2)	(0.6)	(1.4)
Net periodic pension cost/(gain)	$ (1.1)	$ (0.5)	$ (1.3)