Basis of Presentation - Schedule of New Accounting Pronouncements and Changes (Details) - USD ($) $ in Millions	3 Months Ended					6 Months Ended		12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net sales	$ 1,166.7			$ 948.3		$ 2,157.9	$ 1,800.6
Cost of goods sold	818.8			652.8		1,527.1	1,242.5
Selling & administrative expenses	191.0			161.1		374.3	315.9
Operating Income	156.9			134.4		256.5	242.2
Net income	100.3			79.1		158.6	141.9
Accounts receivable, net	779.7	$ 540.3				779.7		$ 540.3
Inventories, net	686.7	634.7				686.7		634.7
Other current assets	64.2	39.6				64.2		39.6
Total Assets	4,971.1	3,720.6				4,971.1		3,720.6
Other accrued liabilities	212.7	174.9				212.7		174.9
Total Liabilities	3,269.3	2,072.7				3,269.3		2,072.7
Retained Earnings	1,967.0	1,892.4				1,967.0		1,892.4
Total Equity	1,701.8	1,647.9		1,603.2		1,701.8	$ 1,603.2	1,647.9	$ 1,603.2
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
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
Balances Without Adoption of ASC 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net sales	1,165.9					2,156.3
Cost of goods sold	818.0					1,525.5
Accounts receivable, net	760.7					760.7
Inventories, net	698.9					698.9
Other current assets	52.7					52.7
Total Assets	4,952.8					4,952.8
Other accrued liabilities	195.0					195.0
Total Liabilities	3,251.6					3,251.6
Retained Earnings	1,966.4					1,966.4
Total Equity	1,701.2					1,701.2
Effect of Adoption Higher/(Lower) | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total net sales	0.8					1.6
Cost of goods sold	0.8					1.6
Accounts receivable, net	(19.0)					(19.0)
Inventories, net	12.2					12.2
Other current assets	(11.5)					(11.5)
Total Assets	(18.3)					(18.3)
Other accrued liabilities	(17.7)					(17.7)
Total Liabilities	(17.7)					(17.7)
Retained Earnings	(0.6)	$ (0.6)				(0.6)		$ (0.6)
Total Equity	$ (0.6)					$ (0.6)