Stockholders' Equity - Changes in Accumulated Other Comprehensive Income by Component (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at January 1, 2017	$ (139.6)
Amounts reclassified from AOCI, net of tax	2.9
Balance at March 31, 2017	(136.7)
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), Net of Tax [Roll Forward]
Balance at January 1, 2017	(121.4)
Amounts reclassified from AOCI, net of tax	2.2
Balance at March 31, 2017	(119.2)
Treasury Lock | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at January 1, 2017	(17.8)
Amounts reclassified from AOCI, net of tax	0.9
Balance at March 31, 2017	(16.9)
Foreign Exchange Contract | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at January 1, 2017	(0.4)
Amounts reclassified from AOCI, net of tax	(0.2)
Balance at March 31, 2017	$ (0.6)