Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Mar. 31, 2020
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	$ 9,177.5	$ 9,482.2
Carrying Amount | Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,907.3	2,373.9
Carrying Amount | Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,692.5	1,708.9
Carrying Amount | Bridge Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	0.0	608.8
Carrying Amount | 4.333% 2023 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	990.5	988.8
Carrying Amount | 3.922% 2021 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	996.1	993.1
Carrying Amount | 2.670% 2023 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	995.7	0.0
Carrying Amount | 4.250% 2025 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,183.9	0.0
Carrying Amount | 2017 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	799.2	1,552.8
Carrying Amount | 2015 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	261.2	910.1
Carrying Amount | 2017 Junior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	351.1	345.8
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	11,352.0	11,090.3
Fair Value | Revolving Credit Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,919.6	2,388.5
Fair Value | Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,705.7	1,723.5
Fair Value | Bridge Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	0.0	615.0
Fair Value | 4.333% 2023 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,077.1	990.0
Fair Value | 3.922% 2021 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,021.8	985.0
Fair Value | 2.670% 2023 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,036.0	0.0
Fair Value | 4.250% 2025 Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,246.8	0.0
Fair Value | 2017 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,608.9	2,130.3
Fair Value | 2015 Senior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	695.9	1,601.8
Fair Value | 2017 Junior Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	$ 1,040.2	$ 656.2