Debt - Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Debt Instrument [Line Items]
Debt issuance cost amortization	$ 7.3	$ 9.5	$ 11.5
Debt discount amortization	37.5	7.2	44.9
Other interest expense	4.5	5.0	5.4
Total interest expense	198.3	203.9	257.0
Senior Indebtedness
Debt Instrument [Line Items]
Debt issuance cost amortization	4.5	6.8	9.1
Debt discount amortization	37.5	7.2	7.0
Interest expense	147.3	179.3	187.1
Total interest expense	189.3	193.3	203.2
Convertible Debt
Debt Instrument [Line Items]
Debt issuance cost amortization	2.8	2.7	2.4
Debt discount amortization	0.0	0.0	37.9
Interest expense	1.7	2.9	8.1
Total interest expense	$ 4.5	$ 5.6	$ 48.4