Debt - Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Debt issuance amortization			$ 9.0	$ 8.5
Debt discount amortization			43.1	60.2
Other interest expense	$ 1.1	$ 0.8	2.1	1.3
Total interest expense	93.3	129.6	192.4	262.2
Senior Secured Indebtedness
Debt Instrument [Line Items]
Debt issuance amortization	3.7	3.3	7.8	6.6
Debt discount amortization	1.6	0.7	3.1	1.4
Interest expense	59.4	74.9	112.1	153.6
Total interest expense	64.7	78.9	123.0	161.6
Convertible Debt
Debt Instrument [Line Items]
Debt issuance amortization	0.5	1.0	1.2	1.9
Debt discount amortization	16.2	29.6	40.0	58.8
Interest expense	10.8	19.3	26.1	38.6
Total interest expense	$ 27.5	$ 49.9	$ 67.3	$ 99.3