Basis of Presentation and Significant Accounting Policies - Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Financial Assets:
Cash equivalents	$ 83.2	$ 330.8
Financial Liabilities:
Derivative instruments	8.8
Convertible senior notes
Financial Liabilities:
Long-term debt	89.1	271.3
Senior Notes due 2022
Financial Liabilities:
Long-term debt	1,479.8
Senior Notes due 2021
Financial Liabilities:
Long-term debt	507.5
Senior Notes due 2019
Financial Liabilities:
Long-term debt	920.3	527.5
Senior Notes due 2018
Financial Liabilities:
Long-term debt	271.0
Term loan facility
Financial Liabilities:
Long-term debt	1,590.0
Senior Debentures due 2034
Financial Liabilities:
Long-term debt	201.0
Euro private placement notes due 2020
Financial Liabilities:
Long-term debt	13.9
Carrying Value
Financial Assets:
Cash equivalents	83.2	330.8
Financial Liabilities:
Derivative instruments	8.8
Carrying Value | Convertible senior notes
Financial Liabilities:
Long-term debt	46.8	89.9
Carrying Value | Senior Notes due 2022
Financial Liabilities:
Long-term debt	1,577.0
Carrying Value | Senior Notes due 2021
Financial Liabilities:
Long-term debt	536.6
Carrying Value | Senior Notes due 2019
Financial Liabilities:
Long-term debt	900.4	490.2
Carrying Value | Senior Notes due 2018
Financial Liabilities:
Long-term debt	268.2
Carrying Value | Term loan facility
Financial Liabilities:
Long-term debt	1,540.3
Carrying Value | Senior Debentures due 2034
Financial Liabilities:
Long-term debt	199.0
Carrying Value | Euro private placement notes due 2020
Financial Liabilities:
Long-term debt	14.5
Level 1
Financial Assets:
Cash equivalents	9.1	330.8
Financial Liabilities:
Derivative instruments	0.0
Level 1 | Convertible senior notes
Financial Liabilities:
Long-term debt	89.1	271.3
Level 1 | Senior Notes due 2022
Financial Liabilities:
Long-term debt	1,479.8
Level 1 | Senior Notes due 2021
Financial Liabilities:
Long-term debt	0.0
Level 1 | Senior Notes due 2019
Financial Liabilities:
Long-term debt	920.3	527.5
Level 1 | Senior Notes due 2018
Financial Liabilities:
Long-term debt	0.0
Level 1 | Term loan facility
Financial Liabilities:
Long-term debt	0.0
Level 1 | Senior Debentures due 2034
Financial Liabilities:
Long-term debt	0.0
Level 1 | Euro private placement notes due 2020
Financial Liabilities:
Long-term debt	0.0
Level 2
Financial Assets:
Cash equivalents	74.1	0.0
Financial Liabilities:
Derivative instruments	8.8
Level 2 | Convertible senior notes
Financial Liabilities:
Long-term debt	0.0	0.0
Level 2 | Senior Notes due 2022
Financial Liabilities:
Long-term debt	0.0
Level 2 | Senior Notes due 2021
Financial Liabilities:
Long-term debt	507.5
Level 2 | Senior Notes due 2019
Financial Liabilities:
Long-term debt	0.0	0.0
Level 2 | Senior Notes due 2018
Financial Liabilities:
Long-term debt	271.0
Level 2 | Term loan facility
Financial Liabilities:
Long-term debt	1,590.0
Level 2 | Senior Debentures due 2034
Financial Liabilities:
Long-term debt	201.0
Level 2 | Euro private placement notes due 2020
Financial Liabilities:
Long-term debt	13.9
Level 3
Financial Assets:
Cash equivalents	0.0	0.0
Financial Liabilities:
Derivative instruments	0.0
Level 3 | Convertible senior notes
Financial Liabilities:
Long-term debt	0.0	0.0
Level 3 | Senior Notes due 2022
Financial Liabilities:
Long-term debt	0.0
Level 3 | Senior Notes due 2021
Financial Liabilities:
Long-term debt	0.0
Level 3 | Senior Notes due 2019
Financial Liabilities:
Long-term debt	0.0	$ 0.0
Level 3 | Senior Notes due 2018
Financial Liabilities:
Long-term debt	0.0
Level 3 | Term loan facility
Financial Liabilities:
Long-term debt	0.0
Level 3 | Senior Debentures due 2034
Financial Liabilities:
Long-term debt	0.0
Level 3 | Euro private placement notes due 2020
Financial Liabilities:
Long-term debt	$ 0.0