Debt - Unamortized Discount and Debt Issuance Costs (Details) - USD ($) $ in Millions	Dec. 31, 2023	Mar. 31, 2023
Debt Instrument [Line Items]
Total unamortized discount	$ (7.2)	$ (10.4)
Total debt issuance costs	(4.6)	(16.3)
Senior Indebtedness | 4.333% 2023 Notes
Debt Instrument [Line Items]
Total unamortized discount	0.0	(0.2)
Total debt issuance costs	0.0	(0.4)
Senior Indebtedness | 2.670% 2023 Notes
Debt Instrument [Line Items]
Total unamortized discount	0.0	(0.4)
Total debt issuance costs	0.0	(0.2)
Senior Indebtedness | 0.972% 2024 Notes
Debt Instrument [Line Items]
Total unamortized discount	(0.2)	(1.2)
Total debt issuance costs	(0.1)	(0.6)
Senior Indebtedness | 0.983% 2024 Notes
Debt Instrument [Line Items]
Total unamortized discount	(0.6)	(1.3)
Total debt issuance costs	(0.4)	(0.8)
Senior Indebtedness | 4.250% 2025 Notes
Debt Instrument [Line Items]
Total unamortized discount	(5.2)	(7.3)
Total debt issuance costs	(0.7)	(0.9)
Senior Convertible Debt | 2017 Senior Convertible Debt
Debt Instrument [Line Items]
Total debt issuance costs	(0.2)	(0.4)
Senior Convertible Debt | 2020 Senior Convertible Debt
Debt Instrument [Line Items]
Total debt issuance costs	(2.4)	(4.4)
Commercial Paper
Debt Instrument [Line Items]
Total unamortized discount	(1.2)	0.0
Term Loan Facility
Debt Instrument [Line Items]
Total debt issuance costs	(0.8)	0.0
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Total debt issuance costs	$ 0.0	$ (8.6)