Debt - Debt Obligations (Details) - USD ($) $ in Millions	Sep. 30, 2023	Mar. 31, 2023
Debt Instrument [Line Items]
Long-term debt	$ 6,099.2	$ 6,466.6
Less: Debt discount	(10.6)	(10.4)
Less: Debt issuance costs	(12.8)	(16.3)
Net long-term debt including current maturities	6,075.8	6,439.9
Less: Current maturities	(1,661.1)	(1,398.2)
Net long-term debt	4,414.7	5,041.7
Senior Indebtedness
Debt Instrument [Line Items]
Long-term debt	5,389.0	5,700.0
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt	39.0	100.0
Less: Debt issuance costs	(7.1)	(8.6)
Line of Credit | Term Loan Facility
Debt Instrument [Line Items]
Long-term debt	750.0	0.0
Less: Debt issuance costs	$ (0.9)	0.0
Senior Indebtedness | 4.333% 2023 Notes
Debt Instrument [Line Items]
Coupon Interest Rate	4.333%
Effective Interest Rate	4.70%
Long-term debt	$ 0.0	1,000.0
Less: Debt discount	0.0	(0.2)
Less: Debt issuance costs	$ 0.0	(0.4)
Senior Indebtedness | 2.670% 2023 Notes
Debt Instrument [Line Items]
Coupon Interest Rate	2.67%
Effective Interest Rate	2.80%
Long-term debt	$ 0.0	1,000.0
Less: Debt discount	0.0	(0.4)
Less: Debt issuance costs	$ 0.0	(0.2)
Senior Indebtedness | 0.972% 2024 Notes
Debt Instrument [Line Items]
Coupon Interest Rate	0.972%
Effective Interest Rate	1.10%
Long-term debt	$ 1,400.0	1,400.0
Less: Debt discount	(0.5)	(1.2)
Less: Debt issuance costs	$ (0.3)	(0.6)
Senior Indebtedness | 0.983% 2024 Notes
Debt Instrument [Line Items]
Coupon Interest Rate	0.983%
Effective Interest Rate	1.10%
Long-term debt	$ 1,000.0	1,000.0
Less: Debt discount	(0.9)	(1.3)
Less: Debt issuance costs	$ (0.4)	(0.8)
Senior Indebtedness | 4.250% 2025 Notes
Debt Instrument [Line Items]
Coupon Interest Rate	4.25%
Effective Interest Rate	4.60%
Long-term debt	$ 1,200.0	1,200.0
Less: Debt discount	(5.9)	(7.3)
Less: Debt issuance costs	(0.8)	(0.9)
Convertible Debt
Debt Instrument [Line Items]
Long-term debt	$ 710.2	766.6
Senior Subordinated Convertible Debt | 2015 Senior Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	1.625%
Effective Interest Rate	1.80%
Long-term debt	$ 6.7	12.4
Senior Subordinated Convertible Debt | 2017 Senior Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	1.625%
Effective Interest Rate	1.80%
Long-term debt	$ 38.0	82.2
Less: Debt issuance costs	$ (0.2)	(0.4)
Senior Subordinated Convertible Debt | 2020 Senior Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	0.125%
Effective Interest Rate	0.50%
Long-term debt	$ 665.5	665.5
Less: Debt issuance costs	$ (3.1)	(4.4)
Junior Subordinated Convertible Debt | 2017 Junior Convertible Debt
Debt Instrument [Line Items]
Coupon Interest Rate	2.25%
Effective Interest Rate	2.30%
Long-term debt	$ 0.0	6.5
Commercial Paper
Debt Instrument [Line Items]
Long-term debt	1,000.0	0.0
Less: Debt discount	$ (3.3)	$ 0.0