Stockholders' Equity - Reclassifications from Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax benefit	$ 8.7	$ 8.5	$ 27.3	$ 18.4
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial loss	(1.9)	(1.4)	(5.7)	(4.1)
Income tax benefit	0.7	0.6	2.1	1.6
Total reclassifications for the period, net of tax	(1.2)	(0.8)	(3.6)	(2.5)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial loss	$ (1.9)	$ (1.4)	$ (5.7)	$ (4.1)