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, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.8	$ 3.0
Interest cost	4.0	4.0
Expected return on plan assets	(3.7)	(4.0)
Amortization of unrecognized prior service cost	0.1	0.1
Recognized actuarial losses	3.8	3.8
Total	$ 7.0	$ 6.9