Summary of Significant Accounting Policies - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ 557.9	$ 546.7	$ 508.3	$ 467.9
Accumulated pension and OPEB liability adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(28.2)	(24.9)
Accumulated other comprehensive loss, Income tax benefit	11.4	13.8
Accumulated unrealized loss on derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(0.6)
Accumulated other comprehensive loss, Income tax benefit	1.6
Accumulated unrealized loss on derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss		0.4
Accumulated other comprehensive loss, Income tax benefit		0.2
Accumulated unrealized foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(95.7)	(64.9)
Accumulated other comprehensive loss, Income tax benefit	1.7	4.5
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (124.5)	$ (89.4)	$ (139.3)	$ (141.4)