Defined benefit pension plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Defined benefit pension plans [Line Items]
Service cost	$ 1.6	$ 1.5	$ 3.3	$ 3.1
Interest cost	5.2	5.5	10.6	11.1
Expected return on plan assets	(5.6)	(5.2)	(11.2)	(10.4)
Recognized net actuarial losses	1.0	1.0	1.9	1.9
Settlements		6.2		6.2
Total	2.2	$ 9.0	4.6	$ 11.9
Pension Plans Defined Benefit [Member]
Defined benefit pension plans [Line Items]
Expected contribution	$ 18.0		$ 18.0