Debt and Credit Facility - Amortization and Interest Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Amortization of debt issuance costs			$ 12.1	$ 5.0
Amortization of debt discount			85.2	79.0
Other interest expense	$ 0.6	$ 0.5	9.7	1.6
Interest Expense	137.6	49.7	366.7	148.7
Other Long-Term Debt
Debt Instrument [Line Items]
Amortization of debt issuance costs	3.6	0.7	9.4	2.3
Amortization of debt discount	0.7	0.0	1.5	0.0
Interest expense	84.2	1.6	201.9	5.0
Total interest expense on debt instruments	88.5	2.3	212.8	7.3
Convertible Debt
Debt Instrument [Line Items]
Amortization of debt issuance costs	0.9	0.9	2.7	2.7
Amortization of debt discount	28.3	26.7	83.7	79.0
Interest expense	19.3	19.3	57.8	58.1
Total interest expense on debt instruments	$ 48.5	$ 46.9	$ 144.2	$ 139.8