CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common Stock and Additional Paid-in-Capital	Common Stock Held in Treasury	Accumulated Other Comprehensive Loss	Retained Earnings
Balance, common stock shares issued (in shares) at Mar. 31, 2017		249,500,000
Beginning balance at Mar. 31, 2017	$ 3,270.7	$ 2,537.6	$ (731.9)	$ (14.4)	$ 1,479.4
Balance, common stock held in treasury (in shares) at Mar. 31, 2017			20,400,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	255.4				255.4
Other comprehensive income (loss)	(3.2)			(3.2)
Proceeds from sales of common stock through employee equity incentive plans (shares)		2,700,000
Proceeds from sales of common stock through employee equity incentive plans	42.0	$ 42.0
Restricted stock unit and stock appreciation right withholdings (shares)		(500,000)
Restricted stock unit and stock appreciation right withholdings	(44.4)	$ (44.4)
Treasury stock used for new issuances (shares)		(2,200,000)	(2,200,000)
Treasury stock used for new issuances		$ (69.3)	$ 69.3
Share-based compensation	93.1	$ 93.1
Shares issued to settle convertible debt (in shares)		3,700,000
Shares issued to settle convertible debt	298.5	$ 298.5
Settlement of convertible debt	(337.7)	(337.7)
Exchange of convertible debt	42.9	$ 42.9
Cash dividend	(337.5)				(337.5)
Balance, common stock shares issued (in shares) at Mar. 31, 2018		253,200,000
Ending balance at Mar. 31, 2018	3,279.8	$ 2,562.7	$ (662.6)	(17.6)	1,397.3
Balance, common stock held in treasury (in shares) at Mar. 31, 2018			18,200,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	355.9				355.9
Other comprehensive income (loss)	(1.4)			(1.4)
Non-cash consideration, exchange of employee stock awards - Microsemi acquisition	53.9	$ 53.9
Proceeds from sales of common stock through employee equity incentive plans (shares)		3,400,000
Proceeds from sales of common stock through employee equity incentive plans	42.6	$ 42.6
Restricted stock unit and stock appreciation right withholdings (shares)		(800,000)
Restricted stock unit and stock appreciation right withholdings	(71.8)	$ (71.8)
Treasury stock used for new issuances (shares)		(2,600,000)	(2,600,000)
Treasury stock used for new issuances		$ (80.4)	$ 80.4
Share-based compensation	172.8	$ 172.8
Cash dividend	$ (344.4)				(344.4)
Balance, common stock shares issued (in shares) at Mar. 31, 2019	253,232,909	253,200,000
Ending balance at Mar. 31, 2019	$ 5,287.5	$ 2,679.8	$ (582.2)	(20.7)	3,210.6
Balance, common stock held in treasury (in shares) at Mar. 31, 2019	15,643,408		15,600,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 570.6				570.6
Other comprehensive income (loss)	0.4			0.4
Proceeds from sales of common stock through employee equity incentive plans (shares)		3,200,000
Proceeds from sales of common stock through employee equity incentive plans	58.8	$ 58.8
Restricted stock unit and stock appreciation right withholdings (shares)		(700,000)
Restricted stock unit and stock appreciation right withholdings	(68.1)	$ (68.1)
Treasury stock used for new issuances (shares)		(2,500,000)	(2,500,000)
Treasury stock used for new issuances		$ (81.6)	$ 81.6
Share-based compensation	172.7	$ 172.7
Shares issued to settle convertible debt (in shares)		5,200,000
Shares issued to settle convertible debt	351.8	$ 351.8
Settlement of convertible debt	(438.1)	$ (438.1)
Cash dividend	$ (350.1)				(350.1)
Balance, common stock shares issued (in shares) at Mar. 31, 2020	258,391,231	258,400,000
Ending balance at Mar. 31, 2020	$ 5,585.5	$ 2,675.3	$ (500.6)	$ (21.6)	$ 3,432.4
Balance, common stock held in treasury (in shares) at Mar. 31, 2020	13,065,588		13,100,000