Pensions and Postretirement Benefits - Schedule of Projected Benefit Obligations Amounts Recognized in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Long-term assets	$ 2.7	$ 0.8
Current liabilities	(0.8)	(0.5)
Long-term liabilities	(11.1)	(18.8)
Underfunded Status at End of Year	(9.2)	(18.5)
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Long-term assets	0.0	0.0
Current liabilities	(0.3)	(0.3)
Long-term liabilities	(3.8)	(4.4)
Underfunded Status at End of Year	$ (4.1)	$ (4.7)