Stockholders' Equity - Reclassifications from Accumulated Other Comprehensive Loss (Details) - Amount Reclassified from Accumulated Other Comprehensive Loss - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses of defined benefit pension plans	[1],[2]	$ (1.0)	$ (0.8)
Total before tax	[1]	(1.0)	(0.8)
Income tax benefit	[1],[2]	0.2	0.3
Total reclassifications for the period, net of tax	[1]	$ (0.8)	$ (0.5)

[1] Amounts in parentheses indicate losses.

[2] Continuing operations only.