Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Deferred tax assets:
Inventory valuation	$ 46.0	$ 48.5
Net operating loss carryforward	68.0	74.8
Capital loss carryforward	6.3	9.4
Share-based compensation	46.5	39.8
Income tax credits	331.1	351.1
Property, plant and equipment	32.7	31.7
Accrued expenses	83.6	80.4
Intangible assets	1,581.5	1,694.8
Lease liabilities	37.1	20.2
Other	17.4	14.0
Gross deferred tax assets	2,250.2	2,364.7
Valuation allowances	(290.3)	(303.5)
Deferred tax assets, net of valuation allowances	1,959.9	2,061.2
Deferred tax liabilities:
Convertible debt	(53.9)	(228.7)
Intangible assets	(158.1)	(365.1)
ROU assets	(34.5)	(24.3)
Other	(8.1)	(13.1)
Deferred tax liabilities	(254.6)	(631.2)
Net deferred tax asset	1,705.3	1,430.0
Reported as:
Non-current deferred tax assets	1,749.2	1,748.5
Non-current deferred tax liability	(43.9)	(318.5)
Net deferred tax asset	$ 1,705.3	$ 1,430.0