Stockholders' Equity - Reconciliation of accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Equity [Roll Forward]
Beginning balance			$ 677.5				$ 677.5
Ending balance	$ 678.3						678.3
Gains and Losses on Cash Flow Hedges
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(3.2)	$ 0.1	0.1	$ 0.3	$ 0.2	$ (0.3)	0.1	$ (0.3)
Other comprehensive income (loss) before reclassifications	(1.2)	(3.6)				0.3
Amounts reclassified from accumulated other comprehensive loss	2.5	0.3			0.1	0.2
Net other comprehensive income (loss)	1.3	(3.3)			0.1	0.5
Ending balance	(1.9)	(3.2)	0.1	0.3	0.3	0.2	(1.9)	0.3
Pension & Postretirement
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(43.7)	(44.4)	(45.1)	(50.7)	(51.2)	(51.8)	(45.1)	(51.8)
Other comprehensive income (loss) before reclassifications	(0.2)	(0.1)	0.1	8.0
Amounts reclassified from accumulated other comprehensive loss	4.4	0.8	0.6	(2.3)	0.5	0.6
Net other comprehensive income (loss)	4.2	0.7	0.7	5.7	0.5	0.6
Ending balance	(39.5)	(43.7)	(44.4)	(45.0)	(50.7)	(51.2)	(39.5)	(45.0)
Foreign Currency Translation
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(67.8)	(41.0)	(52.4)	(77.6)	(100.7)	(110.8)	(52.4)	(110.8)
Other comprehensive income (loss) before reclassifications	(7.1)	(26.8)	11.4	14.2	23.1	10.1
Net other comprehensive income (loss)	(7.1)	(26.8)	11.4	14.2	23.1	10.1
Ending balance	(74.9)	(67.8)	(41.0)	(63.4)	(77.6)	(100.7)	(74.9)	(63.4)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Equity [Roll Forward]
Beginning balance	(114.7)	(85.3)	(97.4)	(128.0)	(151.7)	(162.9)	(97.4)	(162.9)
Other comprehensive income (loss) before reclassifications	(8.5)	(30.5)	11.5	22.2	23.1	10.4
Amounts reclassified from accumulated other comprehensive loss	6.9	1.1	0.6	(2.3)	0.6	0.8
Net other comprehensive income (loss)	(1.6)	(29.4)	12.1	19.9	23.7	11.2
Ending balance	$ (116.3)	$ (114.7)	$ (85.3)	$ (108.1)	$ (128.0)	$ (151.7)	$ (116.3)	$ (108.1)

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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