Debt - Unamortized Discount and Debt Issuance Costs (Details) - USD ($) $ in Millions	Mar. 31, 2026	Feb. 28, 2026	Mar. 31, 2025	May 31, 2024
Debt Instrument [Line Items]
Total unamortized discount	$ (9.3)		$ (13.1)
Total debt issuance costs	(31.2)		(19.5)
Commercial Paper
Debt Instrument [Line Items]
Total unamortized discount	(0.5)		(0.1)
Senior indebtedness \| 4.250% 2025 Notes
Debt Instrument [Line Items]
Total unamortized discount	0.0		(1.3)
Total debt issuance costs	0.0		(0.2)
Senior indebtedness \| 4.900% 2028 Notes
Debt Instrument [Line Items]
Total unamortized discount	(2.2)		(3.3)
Total debt issuance costs	(1.1)		(1.7)
Senior indebtedness \| 5.050% 2029 Notes
Debt Instrument [Line Items]
Total unamortized discount	(3.3)		(4.3)
Total debt issuance costs	(1.2)		(1.8)
Senior indebtedness \| 5.050% 2030 Notes
Debt Instrument [Line Items]
Total unamortized discount	(3.3)		(4.1)
Total debt issuance costs	(1.4)		(1.7)
Senior subordinated convertible debt \| 2017 Senior Convertible Debt
Debt Instrument [Line Items]
Total debt issuance costs	0.0		(0.1)
Senior subordinated convertible debt \| 2024 Senior Convertible Debt
Debt Instrument [Line Items]
Total debt issuance costs	(11.4)		(14.0)	$ (16.5)
Senior subordinated convertible debt \| 2026 Senior Convertible Debt
Debt Instrument [Line Items]
Total debt issuance costs	$ (16.1)	$ (16.6)	$ 0.0