Income Taxes - Schedule of Significant Deferred Tax Assets And Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Components Of Deferred Tax Assets And Liabilities [Abstract]
Pension and other postretirement benefits plan liabilities	$ 58.8	$ 100.1
Net operating losses and other tax carryforwards	255.1	164.9
Accrued liabilities	51.5	86.1
Foreign depreciation	19.4	14.6
Other	16.5	25.1
Total deferred tax assets	401.3	390.8
Valuation allowances	(238.3)	(154.1)
Net deferred tax assets	163.0	236.7
Accelerated depreciation	(45.8)	(68.2)
Other intangible assets	(20.0)	(36.0)
Inventories	(7.3)	(7.6)
Other	(14.0)	(23.1)
Total deferred tax liabilities	(87.1)	(134.9)
Net deferred tax assets	$ 75.9	$ 101.8