Defined Benefit Pension Plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Detail) - Defined Benefit Pension Plans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.5	$ 2.7	$ 9.9	$ 8.3
Interest cost	3.1	4.0	9.0	11.9
Expected return on plan assets	(2.9)	(3.6)	(8.4)	(10.7)
Amortization of prior service cost	0.1	0.1	0.2	0.2
Recognized actuarial losses	5.0	3.7	14.4	11.2
Total	$ 8.8	$ 6.9	$ 25.1	$ 20.9