Stockholders' Equity - Changes in Accumulated Other Comprehensive Income by Component (Details) $ in Millions	6 Months Ended
	Jun. 30, 2016 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance at January 1, 2016	$ (124.9)
Other comprehensive income (loss) before reclassifications, net of tax	3.1
Amounts reclassified from AOCI, net of tax	4.9
Balance at June 30, 2016	(116.9)
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), Net of Tax [Roll Forward]
Balance at January 1, 2016	(103.3)
Other comprehensive income (loss) before reclassifications, net of tax	3.1
Amounts reclassified from AOCI, net of tax	3.2	[1]
Balance at June 30, 2016	(97.0)
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, 2016	(21.2)
Other comprehensive income (loss) before reclassifications, net of tax	0.0
Amounts reclassified from AOCI, net of tax	1.7	[2]
Balance at June 30, 2016	(19.5)
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, 2016	(0.4)
Other comprehensive income (loss) before reclassifications, net of tax	0.0
Amounts reclassified from AOCI, net of tax	0.0
Balance at June 30, 2016	$ (0.4)

[1] These AOCI components are included in the computation of net pension and postretirement benefit costs. See Note 10, Employee Benefit Plans and Other Postretirement Benefits, for additional information.

[2] This AOCI component is included in interest expense, net. Amount relates to the amortization of the effective portion of treasury lock derivative instruments recorded in AOCI. The net amount of settlement gains or losses on derivative instruments included in AOCI to be amortized over the next 12 months is a net loss of $5.7 million ($3.5 million after tax). For a discussion of treasury lock derivative instrument activity, see Note 14, Derivative Instruments and Hedging Activities, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2015 Annual Report on Form 10-K.