Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	$ (24.0)	$ (21.6)
Income before taxes	179.1	159.2
Income tax benefit	(61.7)	(55.5)
Net income	117.4	103.7
Unfunded Employee Benefit Obligations | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service costs	(1.5)	(1.4)
Amortization of actuarial losses	(1.9)	(1.2)
Income before taxes	(3.4)	(2.6)
Income tax benefit	1.2	1.0
Net income	(2.2)	(1.6)
Treasury Lock | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net	(1.4)	(1.4)
Income tax benefit	0.5	0.5
Net income	$ (0.9)	$ (0.9)