Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Other expense, net $ (2.0) $ 0.7 $ (3.5) $ 1.9
Interest expense, net (23.4) (21.7) (67.5) (63.2)
Income before taxes 183.0 197.7 519.9 510.9
Income tax benefit (63.7) (69.9) (181.0) (178.3)
Net income 119.3 127.8 338.9 332.6
Accumulated Foreign Currency Adjustment Attributable to Parent        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Income tax benefit 0.0 0.0 0.0 0.0
Net income 0.0 0.0 0.0 (4.2)
Accumulated Foreign Currency Adjustment Attributable to Parent | Reclassification out of Accumulated Other Comprehensive Income [Member]        
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]        
Other expense, net 0.0 0.0 0.0 (4.2)
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 (1.3) [1] (1.4) [1] (4.2) (4.2)
Amortization of actuarial losses (1.5) [1] (2.1) [1] (3.9) (6.5)
Income before taxes (2.8) (3.5) (8.1) (10.7)
Income tax benefit 1.0 1.4 3.1 4.2
Net income (1.8) (2.1) (5.0) (6.5)
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 [2] (1.4) (1.4) (4.2) (4.2)
Income tax benefit 0.5 0.5 1.6 1.6
Net income $ (0.9) $ (0.9) $ (2.6) $ (2.6)
[1] These AOCI components are included in the computation of net pension and postretirement benefit costs. See Note 11, 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.