Debt - Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Debt Instrument [Line Items]
Debt issuance amortization	$ 17.1	$ 16.5	$ 6.6
Debt discount amortization	121.7	114.6	106.1
Other interest expense	3.7	2.9	2.4
Total interest expense	497.3	502.9	199.0
Senior Secured Indebtedness
Debt Instrument [Line Items]
Debt issuance amortization	13.2	12.9	3.1
Debt discount amortization	2.9	2.2	0.0
Interest expense	277.6	291.8	6.6
Total interest expense	293.7	306.9	9.7
Convertible Debt
Debt Instrument [Line Items]
Debt issuance amortization	3.9	3.6	3.5
Debt discount amortization	118.8	112.4	106.1
Interest expense	77.2	77.1	77.3
Total interest expense	$ 199.9	$ 193.1	$ 186.9