CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Microsemi Corporation	Common Stock and Additional Paid-in-Capital	Common Stock and Additional Paid-in-Capital Atmel Corporation	Common Stock and Additional Paid-in-Capital Microsemi Corporation	Common Stock Held in Treasury	Accumulated Other Comprehensive Income	Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative adjustment | Accounting Standards Update 2016-09	$ 49.6		$ 2.0					$ 47.6
Balance at Mar. 31, 2016	2,151.0		$ 1,391.9			$ (820.1)	$ (3.4)	1,582.6
Balance, common stock shares issued (in shares) at Mar. 31, 2016			227,400,000
Balance, common stock held in treasury (in shares) at Mar. 31, 2016						23,400,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	164.6							164.6
Other comprehensive income (loss)	(11.0)						(11.0)
Issuance of common stock - Amtel acquisition (shares)				10,100,000
Issuance of common stock - Atmel acquisition	486.2			$ 486.2
Non-cash consideration, exchange of employee stock awards	7.5			$ 7.5
Proceeds from sales of common stock through employee equity incentive plans (shares)			4,000,000.0
Proceeds from sales of common stock through employee equity incentive plans	42.2		$ 42.2
Restricted stock unit and stock appreciation right withholdings (shares)			(1,000,000.0)
Restricted stock unit and stock appreciation right withholdings	(58.4)		$ (58.4)
Treasury stock used for new issuances (shares)			(3,000,000.0)			(3,000,000.0)
Treasury stock used for new issuances	0.0		$ (88.2)			$ 88.2
Share-based compensation	127.3		$ 127.3
Shares issued to settle convertible debt (in shares)			12,000,000.0
Shares issued to settle convertible debt	862.7		$ 862.7
Settlement of convertible debt	(850.8)		(850.8)
Convertible Debt - issuance of debt	615.2		615.2
Cash dividend	(315.4)							(315.4)
Balance at Mar. 31, 2017	3,270.7		$ 2,537.6			$ (731.9)	(14.4)	1,479.4
Balance, common stock shares issued (in shares) at Mar. 31, 2017			249,500,000
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	0.0		$ (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)
Convertible Debt - issuance of debt	42.9		42.9
Cash dividend	(337.5)							(337.5)
Balance at Mar. 31, 2018	$ 3,279.8		$ 2,562.7			$ (662.6)	(17.6)	1,397.3
Balance, common stock shares issued (in shares) at Mar. 31, 2018	253,232,909		253,200,000
Balance, common stock held in treasury (in shares) at Mar. 31, 2018	18,205,142					18,200,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative adjustment | Accounting Standards Update 2016-01							(1.7)	1.7
Cumulative adjustment | Accounting Standards Update 2014-09	$ 242.0							242.0
Cumulative adjustment | Accounting Standards Update 2016-16	1,558.1							1,558.1
Net income	355.9	$ (570.8)						355.9
Other comprehensive income (loss)	(1.4)						(1.4)
Non-cash consideration, exchange of employee stock awards	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	0.0		$ (80.4)			$ 80.4
Share-based compensation	172.8		172.8
Cash dividend	(344.4)							(344.4)
Balance at Mar. 31, 2019	$ 5,287.5		$ 2,679.8			$ (582.2)	$ (20.7)	$ 3,210.6
Balance, common stock shares issued (in shares) at Mar. 31, 2019	253,232,909		253,200,000
Balance, common stock held in treasury (in shares) at Mar. 31, 2019	15,643,408					15,600,000