Retirement Plans and Other Post-Retirement Benefits - Schedule of Net Periodic Benefit Cost of Pension and Other Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.3	$ 2.0	$ 1.8
Interest cost	13.3	13.7	14.0
Expected return on plan assets	(21.1)	(22.2)	(23.3)
Amortization of actuarial loss	7.1	7.1	7.6
One-time settlement charge			7.3
Total net periodic benefit cost	1.6	0.6	7.4
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1
Interest cost	0.5	0.4	0.4
Amortization of actuarial loss	(0.3)		(0.1)
Total net periodic benefit cost	$ 0.3	$ 0.5	$ 0.4