Retirement Plans and Other Post-Retirement Benefits - Summary of Amounts Recognized in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	$ 72.3	$ 58.7
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(50.7)	(47.9)
Other Assets [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	115.5	96.7
Current Liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(2.2)	(2.0)
Current Liabilities [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(3.5)	(3.2)
Other Long-Term Liabilities [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	(41.0)	(36.0)
Other Long-Term Liabilities [Member] | Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net amount recognized	$ (47.2)	$ (44.7)