Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Mar. 31, 2023
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	$ 6,075.8	$ 6,439.9
Carrying Amount | Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	996.7	0.0
Carrying Amount | Revolving Credit Facility | Line of Credit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	31.9	91.4
Carrying Amount | Term Loan Facility | Line of Credit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	749.1	0.0
Carrying Amount | 4.333% 2023 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	0.0	999.4
Carrying Amount | 2.670% 2023 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	0.0	999.4
Carrying Amount | 0.972% 2024 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,399.2	1,398.2
Carrying Amount | 0.983% 2024 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	998.7	997.9
Carrying Amount | 4.250% 2025 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,193.3	1,191.8
Carrying Amount | 2015 Senior Convertible Debt | Senior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	6.7	12.4
Carrying Amount | 2017 Senior Convertible Debt | Senior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	37.8	81.8
Carrying Amount | 2020 Senior Convertible Debt | Senior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	662.4	661.1
Carrying Amount | 2017 Junior Convertible Debt | Junior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	0.0	6.5
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	6,082.7	6,516.0
Fair Value | Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,000.0	0.0
Fair Value | Revolving Credit Facility | Line of Credit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	39.0	100.0
Fair Value | Term Loan Facility | Line of Credit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	750.0	0.0
Fair Value | 4.333% 2023 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	0.0	997.1
Fair Value | 2.670% 2023 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	0.0	985.4
Fair Value | 0.972% 2024 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,374.1	1,337.6
Fair Value | 0.983% 2024 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	955.1	941.9
Fair Value | 4.250% 2025 Notes | Senior Indebtedness
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	1,162.9	1,176.0
Fair Value | 2015 Senior Convertible Debt | Senior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	23.6	41.8
Fair Value | 2017 Senior Convertible Debt | Senior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	84.1	189.6
Fair Value | 2020 Senior Convertible Debt | Senior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	693.9	732.1
Fair Value | 2017 Junior Convertible Debt | Junior Subordinated Convertible Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure for debt obligations	$ 0.0	$ 14.5