Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Deferred tax assets:
Inventory valuation	$ 48.5	$ 45.0
Net operating loss carryforward	74.8	94.3
Capital loss carryforward	9.4	9.6
Share-based compensation	39.8	42.4
Income tax credits	351.1	376.5
Property, plant and equipment	31.7	23.6
Accrued expenses and other	80.4	91.4
Intangible assets	1,694.8	1,608.1
Lease liabilities	20.2
Other	14.0	12.6
Gross deferred tax assets	2,364.7	2,303.5
Valuation allowances	(303.5)	(332.1)
Deferred tax assets, net of valuation allowances	2,061.2	1,971.4
Deferred tax liabilities:
Convertible debt	(228.7)	(279.3)
Intangible assets	(365.1)	(721.0)
ROU assets	(24.3)
Deferred tax liabilities	(631.2)	(1,000.3)
Other	(13.1)	0.0
Net deferred tax asset	1,430.0	971.1
Reported as:
Non-current deferred tax assets	1,748.5	1,677.2
Non-current deferred tax liability	(318.5)	(706.1)
Net deferred tax asset	$ 1,430.0	$ 971.1