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, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3.2	$ 2.8
Interest cost	3.0	4.0
Expected return on plan assets	(2.8)	(3.7)
Amortization of unrecognized prior service cost		0.1
Recognized actuarial losses	4.8	3.8
Total	$ 8.2	$ 7.0