Benefit Plans (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Retirement Benefits [Abstract]
Service cost	$ 0.8	$ 0.7	$ 1.6	$ 1.4
Interest cost	0.7	2.7	1.4	5.4
Expected return on plan assets	(0.2)	(1.7)	(0.4)	(3.4)
Pension settlement gain	0.0	12.2	0.0	12.2
Net periodic benefit cost	$ 1.3	$ (10.5)	$ 2.6	$ (8.8)