Retirement Plans and Other Post-Retirement Benefits - Summary of Amounts Recognized in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	$ 1.0	$ 25.8
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(9.2)	(9.7)
Other Assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	43.3	66.4
Current Liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(2.1)	(2.2)
Current Liabilities [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(2.4)	(3.5)
Other Long-Term Liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(40.2)	(38.4)
Other Long-Term Liabilities [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	$ (6.8)	$ (6.2)