Defined Benefit Pension Plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Detail) - Defined Benefit Pension Plans - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.8	$ 3.2
Interest cost	2.4	3.0
Expected return on plan assets	(3.4)	(2.8)
Recognized actuarial losses	5.4	4.8
Total	$ 8.2	$ 8.2