Revenue Recognition - Summary of Impacts of Adopting ASC 606 Condensed Consolidated Statements of Cash Flow (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net income	$ 17.4	$ 0.8	$ 28.0	$ 15.8
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Deferred income taxes			8.2	6.0
Other non cash adjustments			24.7
Change in operating assets and liabilities:
Receivables			(127.0)	(101.4)
Inventories			(94.3)	(75.8)
Other assets			(0.9)	(1.8)
Accounts payable			145.5	68.7
Accrued liabilities			13.6	0.4
Accrued taxes payable/receivable			2.6	(1.1)
Deferred employee benefit costs			(18.3)	(16.0)
Net adjustments			(45.9)	(97.3)
Net cash used in operating activities			(17.9)	$ (81.5)
Adjustments [Member] | ASU 606 [Member]
Operating activities:
Net income	(0.5)		(0.8)
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Deferred income taxes			(0.3)
Change in operating assets and liabilities:
Inventories			3.7
Other assets			(2.7)
Accrued liabilities			0.1
Net adjustments			0.8
Balance without Adoption of ASC 606 [Member]
Operating activities:
Net income	$ 16.9		27.2
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Deferred income taxes			7.9
Other non cash adjustments			24.7
Change in operating assets and liabilities:
Receivables			(127.0)
Inventories			(90.6)
Other assets			(3.6)
Accounts payable			145.5
Accrued liabilities			13.7
Accrued taxes payable/receivable			2.6
Deferred employee benefit costs			(18.3)
Net adjustments			(45.1)
Net cash used in operating activities			$ (17.9)