Debt - Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Debt Instrument [Line Items]
Debt issuance cost amortization	$ 17.1	$ 17.1	$ 16.5
Debt discount amortization	71.1	121.7	114.6
Other interest expense	3.7	3.7	2.9
Total interest expense	356.9	497.3	502.9
Senior Secured Indebtedness
Debt Instrument [Line Items]
Debt issuance cost amortization	14.7	13.2	12.9
Debt discount amortization	6.6	2.9	2.2
Interest expense	227.4	277.6	291.8
Total interest expense	248.7	293.7	306.9
Convertible Debt
Debt Instrument [Line Items]
Debt issuance cost amortization	2.4	3.9	3.6
Debt discount amortization	64.5	118.8	112.4
Interest expense	37.6	77.2	77.1
Total interest expense	$ 104.5	$ 199.9	$ 193.1