Stockholders' Equity - Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2015	$ (124.9)
Other comprehensive income (loss) before reclassifications, net of tax	(24.9)
Amounts reclassified from AOCI, net of tax	10.2
Other comprehensive income (loss)	(14.7)	$ 29.0	$ (88.9)
Balance at December 31, 2016	(139.6)	(124.9)
Net amount of settlement gains (losses) on derivative instruments included in accumulated OCI to be amortized over next 12 months, before tax	(5.7)
Net amount of settlement gains (losses) on derivative instruments included in accumulated OCI to be amortized over next 12 months, after tax	(3.5)
Unfunded Employee Benefit Obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2015	(103.3)
Other comprehensive income (loss) before reclassifications, net of tax	(24.9)
Amounts reclassified from AOCI, net of tax	6.7
Other comprehensive income (loss)	(18.2)
Balance at December 31, 2016	(121.5)	(103.3)
Treasury Lock | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2015	(21.2)
Other comprehensive income (loss) before reclassifications, net of tax	0.0
Amounts reclassified from AOCI, net of tax	3.5
Other comprehensive income (loss)	3.5
Balance at December 31, 2016	(17.7)	(21.2)
Foreign Exchange Contract | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2015	(0.4)
Other comprehensive income (loss) before reclassifications, net of tax	0.0
Amounts reclassified from AOCI, net of tax	0.0
Other comprehensive income (loss)	0.0
Balance at December 31, 2016	$ (0.4)	$ (0.4)