Present and Prospective Accounting Pronouncements Effect of change related to ASU 2017-07 and other reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales	$ 524.0	$ 507.7	$ 1,588.7	$ 1,502.3
Depreciation and amortization	30.7	31.1	91.8	91.3
Selling, general and administrative expense	51.2	49.3	151.9	145.3
Income from operations	167.6	161.5	509.8	373.0
Total non-operating income (expense)	$ (0.6)	(4.2)	$ (3.5)	(14.8)
Scenario, Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales (exclusive of depreciation and amortization shown separately below)		478.3		1,416.3
Depreciation and amortization		31.1		91.3
Selling, general and administrative expense		49.2		144.8
Income from operations		159.9		368.2
Total non-operating income (expense)		(2.6)		(10.0)
Reclassifications other than adoptions [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Depreciation and amortization		0.0		0.0
Reclassifications other than adoptions [Member] | Scenario, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		30.4		89.1
Depreciation and amortization		(31.1)		(91.3)
Selling, general and administrative expense		0.7		2.2
Income from operations		0.0		0.0
Total non-operating income (expense)		0.0		0.0
Accounting Standards Update 2017-07 [Member] | Scenario, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		(1.0)		(3.1)
Depreciation and amortization		0.0		0.0
Selling, general and administrative expense		(0.6)		(1.7)
Income from operations		1.6		4.8
Total non-operating income (expense)		$ (1.6)		$ (4.8)