Benefit Plans - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 0.7	$ 1.0
Interest cost	2.7	3.0
Expected return on plan assets	(1.7)	(2.2)
Net periodic benefit cost	$ 1.7	$ 1.8