Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	$ 1,603.2
Other comprehensive income (loss)	32.7	$ (78.3)	$ (59.9)
End of period	1,647.9	1,603.2
Cash Flow Hedge (Loss) Gain
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	0.0	1.4	0.0
Other comprehensive income (loss) before Reclassifications	(1.7)	(1.4)	1.7
Amounts reclassified from accumulated other comprehensive loss	0.9	0.0	(0.3)
Other comprehensive income (loss)	(0.8)	(1.4)	1.4
End of period	(0.8)	0.0	1.4
Unrealized Gain (Loss) on Available-for-Sale Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(1.2)	0.0	0.3
Other comprehensive income (loss) before Reclassifications	0.6	(1.2)	(0.3)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0
Other comprehensive income (loss)	0.6	(1.2)	(0.3)
End of period	(0.6)	(1.2)	0.0
Pension and Post Retirement Benefit Plan Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(180.5)	(140.2)	(124.7)
Other comprehensive income (loss) before Reclassifications	(3.4)	(48.5)	(22.5)
Amounts reclassified from accumulated other comprehensive loss	7.4	8.2	7.0
Other comprehensive income (loss)	4.0	(40.3)	(15.5)
End of period	(176.5)	(180.5)	(140.2)
Cumulative Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(120.8)	(85.4)	(39.9)
Other comprehensive income (loss) before Reclassifications	28.9	(35.4)	(45.5)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0
Other comprehensive income (loss)	28.9	(35.4)	(45.5)
End of period	(91.9)	(120.8)	(85.4)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(302.5)	(224.2)	(164.3)
Other comprehensive income (loss) before Reclassifications	24.4	(86.5)	(66.6)
Amounts reclassified from accumulated other comprehensive loss	8.3	8.2	6.7
Other comprehensive income (loss)	32.7	(78.3)	(59.9)
End of period	$ (269.8)	$ (302.5)	$ (224.2)