Retirement Plans and Other Post-Retirement Benefits - Summary of Amounts Recognized in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	$ 7.7	$ 1.0
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(6.5)	(9.2)
Cash and Cash Equivalents [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	53.4
Other Assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized		43.3
Current Liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(2.3)	(2.1)
Current Liabilities [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(1.4)	(2.4)
Other Long-Term Liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(43.4)	(40.2)
Other Long-Term Liabilities [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	$ (5.1)	$ (6.8)