CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales		$ 5,349.5	$ 3,980.8	$ 3,407.8
Cost of sales	[1]	2,418.2	1,560.1	1,650.6
Gross profit		2,931.3	2,420.7	1,757.2
Operating expenses:
Research and development	[1]	826.3	529.3	545.3
Selling, general and administrative	[1]	682.9	452.1	499.8
Amortization of acquired intangible assets		674.1	485.5	337.7
Special charges and other, net	[1]	33.7	17.5	98.6
Operating expenses		2,217.0	1,484.4	1,481.4
Operating income		714.3	936.3	275.8
Losses on equity method investments		(0.2)	(0.2)	(0.2)
Other income (expense):
Interest income		8.1	22.0	3.1
Interest expense		(502.9)	(199.0)	(146.3)
Loss on settlement of debt		(12.6)	(16.0)	(43.9)
Other (loss) income, net		(2.2)	(5.8)	1.3
Income before income taxes		204.5	737.3	89.8
Income tax (benefit) provision		(151.4)	481.9	(80.8)
Net income from continuing operations		355.9	255.4	170.6
Discontinued operations:
Loss from discontinued operations		0.0	0.0	(7.6)
Income tax benefit		0.0	0.0	(1.6)
Net loss from discontinued operations		0.0	0.0	(6.0)
Net Income		$ 355.9	$ 255.4	$ 164.6
Basic net income per common share
Basic net income per common share from continuing operations (in dollars per share)		$ 1.51	$ 1.10	$ 0.79
Basic net loss per common share from discontinued operations (in dollars per share)		0	0	(0.03)
Basic net income per common share (in dollars per share)		1.51	1.10	0.76
Diluted net income per common share
Diluted net income per common share from continuing operations (in dollars per share)		1.42	1.03	0.73
Diluted net loss per common share from discontinued operations (in dollars per share)		0	0	(0.02)
Diluted net income per common share (in dollars per share)		1.42	1.03	0.71
Dividends declared per common share (in dollars per share)		$ 1.457	$ 1.449	$ 1.441
Basic common shares outstanding (in shares)		236.2	232.9	217.2
Diluted common shares outstanding (in shares)		249.9	248.9	234.8

[1] (1) Includes share-based compensation expense as follows: Cost of sales$14.9 $13.8 $18.7Research and development$72.0 $42.5 $46.8Selling, general and administrative$62.3 $36.9 $62.6Special charges and other, net$17.2 $— $—