Basis of Presentation - Schedule of New Accounting Pronouncements and Changes (Details) - USD ($) $ in Millions	3 Months Ended					9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net sales	$ 1,179.7		$ 950.5			$ 3,337.6	$ 2,751.1
Costs and expenses
Cost of goods sold	830.7		642.9			2,357.8	1,885.4
Selling & administrative expenses	185.2		157.5			559.5	473.4
Operating Income	163.8		150.1			420.3	392.3
Net income	113.6		80.8			272.2	222.7
ASSETS
Accounts receivable, net	788.2	$ 540.3				788.2		$ 540.3
Inventories, net	672.5	634.7				672.5		634.7
Other current assets	59.4	39.6				59.4		39.6
Total Assets	4,997.5	3,720.6				4,997.5		3,720.6
LIABILITIES
Other accrued liabilities	214.1	174.9				214.1		174.9
Total Liabilities	3,225.7	2,072.7				3,225.7		2,072.7
EQUITY
Retained earnings	2,034.1	1,892.4				2,034.1		1,892.4
Total Equity	1,771.8	1,647.9	1,667.7			1,771.8	$ 1,667.7	1,647.9	$ 1,603.2
Accounting Standards Update 2017-07
Costs and expenses
Cost of goods sold		(0.9)	(0.8)	$ (0.8)	$ (0.8)			(3.3)
Selling & administrative expenses		(2.9)	(3.0)	(3.0)	(2.9)			(11.8)
Total operating expenses		(3.8)	(3.8)	(3.8)	(3.7)			(15.1)
Operating Income		3.8	3.8	3.8	3.7			15.1
Total other expense		(3.8)	(3.8)	(3.8)	(3.7)			(15.1)
Net income		0.0	$ 0.0	$ 0.0	$ 0.0			0.0
Accounting Standards Update 2014-09 | Balances Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net sales	1,179.0					3,335.3
Costs and expenses
Cost of goods sold	830.0					2,355.5
ASSETS
Accounts receivable, net	769.6					769.6
Inventories, net	684.6					684.6
Other current assets	48.2					48.2
Total Assets	4,979.8					4,979.8
LIABILITIES
Other accrued liabilities	197.0					197.0
Total Liabilities	3,208.6					3,208.6
EQUITY
Retained earnings	2,033.5					2,033.5
Total Equity	1,771.2					1,771.2
Accounting Standards Update 2014-09 | Effect of Adoption Higher/(Lower)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net sales	0.7					2.3
Costs and expenses
Cost of goods sold	0.7					2.3
ASSETS
Accounts receivable, net	18.6					18.6
Inventories, net	(12.1)					(12.1)
Other current assets	11.2					11.2
Total Assets	17.7					17.7
LIABILITIES
Other accrued liabilities	17.1					17.1
Total Liabilities	17.1					17.1
EQUITY
Retained earnings	0.6	$ (0.6)				0.6		$ (0.6)
Total Equity	$ 0.6					$ 0.6