Basis of Presentation and Significant Accounting Policies - Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative instruments	$ 42.8	$ 8.8
Convertible senior notes
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Debt instrument, interest rate, stated percentage	4.50%
Long-term debt	$ 98.9	89.1
Senior Notes due 2022
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	1,568.0	1,479.8
Senior Notes due 2021
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	541.5	507.5
Senior Notes due 2019
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	936.0	920.3
Senior Notes due 2018
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	272.1	271.0
Term loan facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	1,600.0	1,590.0
Senior Debentures due 2034
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	219.0	201.0
Euro private placement notes due 2020
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	14.9	13.9
Level 1
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative instruments	0.0	0.0
Level 1 | Convertible senior notes
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	98.9	89.1
Level 1 | Senior Notes due 2022
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	1,568.0	1,479.8
Level 1 | Senior Notes due 2021
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 1 | Senior Notes due 2019
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	936.0	920.3
Level 1 | Senior Notes due 2018
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	272.1	0.0
Level 1 | Term loan facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 1 | Senior Debentures due 2034
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	219.0	0.0
Level 1 | Euro private placement notes due 2020
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 2
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative instruments	42.8	8.8
Level 2 | Convertible senior notes
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 2 | Senior Notes due 2022
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 2 | Senior Notes due 2021
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	541.5	507.5
Level 2 | Senior Notes due 2019
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 2 | Senior Notes due 2018
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	271.0
Level 2 | Term loan facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	1,600.0	1,590.0
Level 2 | Senior Debentures due 2034
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	201.0
Level 2 | Euro private placement notes due 2020
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	14.9	13.9
Level 3
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative instruments	0.0	0.0
Level 3 | Convertible senior notes
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 3 | Senior Notes due 2022
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 3 | Senior Notes due 2021
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 3 | Senior Notes due 2019
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 3 | Senior Notes due 2018
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 3 | Term loan facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 3 | Senior Debentures due 2034
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Level 3 | Euro private placement notes due 2020
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	0.0	0.0
Cash equivalents
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash equivalents	93.3	83.2
Cash equivalents | Level 1
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash equivalents	29.6	9.1
Cash equivalents | Level 2
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash equivalents	63.7	74.1
Cash equivalents | Level 3
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash equivalents	0.0	0.0
Carrying Value
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Derivative instruments	42.8	8.8
Carrying Value | Convertible senior notes
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	47.5	46.8
Carrying Value | Senior Notes due 2022
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	1,577.7	1,577.0
Carrying Value | Senior Notes due 2021
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	561.5	536.6
Carrying Value | Senior Notes due 2019
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	900.3	900.4
Carrying Value | Senior Notes due 2018
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	268.0	268.2
Carrying Value | Term loan facility
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	1,537.9	1,540.3
Carrying Value | Senior Debentures due 2034
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	199.5	199.0
Carrying Value | Euro private placement notes due 2020
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Long-term debt	15.0	14.5
Carrying Value | Cash equivalents
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash equivalents	$ 93.3	$ 83.2