Defined benefit pension plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Defined benefit pension plans [Line Items]
Service cost	$ 1.5	$ 1.6	$ 2.9	$ 3.3
Interest cost	5.8	5.2	11.3	10.6
Expected return on plan assets	(5.9)	(5.6)	(11.4)	(11.2)
Recognized net actuarial losses	0.9	1.0	1.6	1.9
Total	2.3	$ 2.2	4.4	$ 4.6
Defined benefit plan pension asset	21.9		21.9		$ 19.8
Pension plans defined benefit
Defined benefit pension plans [Line Items]
Expected contribution	$ 16.0		$ 16.0
Pension plans defined benefit | United States
Defined benefit pension plans [Line Items]
Defined benefit plan benefit obligation					65.2
Defined benefit plan fair value of plan assets					75.7
Defined benefit plan pension asset					$ 10.7