Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Retirement Benefits [Abstract]
Service cost	$ 0.7	$ 1.0	$ 1.8	$ 3.1
Interest cost	0.9	3.0	6.3	9.0
Expected return on plan assets	(0.2)	(2.2)	(3.6)	(6.7)
Actuarial gain	0.4	2.2	(11.8)	2.2
Net periodic benefit cost	$ 1.8	$ 4.0	$ (7.3)	$ 7.6