Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Components of Deferred Tax Assets [Abstract]
Deferred income on shipments to distributors	$ 0.0		$ 39.1
Inventory valuation	45.0		10.7
Net operating loss carryforward	94.3		101.1
Capital loss carryforward	9.6		10.6
Share-based compensation	42.4		31.4
Income tax credits	376.5		178.4
Property, plant and equipment	23.6		25.7
Accrued expenses and other	91.4		91.2
Intangible assets	1,608.1		0.0
Other	12.6		0.0
Gross deferred tax assets	2,303.5		488.2
Valuation allowances	(332.1)		(204.5)
Deferred tax assets, net of valuation allowances	1,971.4		283.7
Components of Deferred Tax Liabilities [Abstract]
Convertible debt	(279.3)		(304.4)
Intangible assets	(721.0)		(66.6)
Other	0.0		(18.3)
Deferred tax liabilities	(1,000.3)		(389.3)
Net deferred tax asset	971.1
Net deferred tax liability			(105.6)
Non-current deferred tax assets	1,677.2	$ 1,656.5	100.2
Non-current deferred tax liability	$ (706.1)	$ (221.5)	$ (205.8)