CONDENSED 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 Income	Retained Earnings
Balance, common stock shares issued (in shares) at Mar. 31, 2018		253,200,000
Beginning 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	35.7				35.7
Other comprehensive income (loss)	4.4			4.4
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)		700,000
Proceeds from sales of common stock through employee equity incentive plans	6.4	$ 6.4
Restricted stock unit and stock appreciation right withholdings (shares)		(200,000)
Restricted stock unit and stock appreciation right withholdings	(16.8)	$ (16.8)
Treasury stock used for new issuances (shares)		(500,000)	(500,000)
Treasury stock used for new issuances	0.0	$ (14.9)	$ 14.9
Share-based compensation	45.9	$ 45.9
Cash dividend	(85.5)				(85.5)
Balance, common stock shares issued (in shares) at Jun. 30, 2018		253,200,000
Ending balance at Jun. 30, 2018	5,123.8	$ 2,637.2	$ (647.7)	(14.9)	3,149.2
Balance, common stock held in treasury (in shares) at Jun. 30, 2018			17,700,000
Balance, common stock shares issued (in shares) at Mar. 31, 2018		253,200,000
Beginning 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	132.0
Other comprehensive income (loss)	2.6
Balance, common stock shares issued (in shares) at Sep. 30, 2018		253,200,000
Ending balance at Sep. 30, 2018	5,170.2	$ 2,652.7	$ (625.4)	(16.7)	3,159.6
Balance, common stock held in treasury (in shares) at Sep. 30, 2018			17,000,000.0
Balance, common stock shares issued (in shares) at Jun. 30, 2018		253,200,000
Beginning balance at Jun. 30, 2018	5,123.8	$ 2,637.2	$ (647.7)	(14.9)	3,149.2
Balance, common stock held in treasury (in shares) at Jun. 30, 2018			17,700,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	96.3				96.3
Other comprehensive income (loss)	(1.8)			(1.8)
Proceeds from sales of common stock through employee equity incentive plans (shares)		900,000
Proceeds from sales of common stock through employee equity incentive plans	13.9	$ 13.9
Restricted stock unit and stock appreciation right withholdings (shares)		(200,000)
Restricted stock unit and stock appreciation right withholdings	(20.1)	$ (20.1)
Treasury stock used for new issuances (shares)		(700,000)	(700,000)
Treasury stock used for new issuances	0.0	$ (22.3)	$ 22.3
Share-based compensation	44.0	$ 44.0
Cash dividend	(85.9)				(85.9)
Balance, common stock shares issued (in shares) at Sep. 30, 2018		253,200,000
Ending balance at Sep. 30, 2018	$ 5,170.2	$ 2,652.7	$ (625.4)	(16.7)	3,159.6
Balance, common stock held in treasury (in shares) at Sep. 30, 2018			17,000,000.0
Balance, common stock shares issued (in shares) at Mar. 31, 2019	253,232,909	253,200,000
Beginning 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	$ 50.7				50.7
Other comprehensive income (loss)	(0.3)			(0.3)
Proceeds from sales of common stock through employee equity incentive plans (shares)		500,000
Proceeds from sales of common stock through employee equity incentive plans	7.3	$ 7.3
Restricted stock unit and stock appreciation right withholdings (shares)		(100,000)
Restricted stock unit and stock appreciation right withholdings	(11.4)	$ (11.4)
Treasury stock used for new issuances (shares)		(400,000)	(400,000)
Treasury stock used for new issuances	0.0	$ (13.8)	$ 13.8
Share-based compensation	41.6	$ 41.6
Cash dividend	(87.1)				(87.1)
Balance, common stock shares issued (in shares) at Jun. 30, 2019		253,200,000
Ending balance at Jun. 30, 2019	$ 5,288.3	$ 2,703.5	$ (568.4)	(22.3)	3,175.5
Balance, common stock held in treasury (in shares) at Jun. 30, 2019			15,200,000
Balance, common stock shares issued (in shares) at Mar. 31, 2019	253,232,909	253,200,000
Beginning 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	$ 159.6
Other comprehensive income (loss)	$ (0.3)			(0.3)
Balance, common stock shares issued (in shares) at Sep. 30, 2019	253,232,909	253,200,000
Ending balance at Sep. 30, 2019	$ 5,361.3	$ 2,731.7	$ (545.2)	(22.3)	3,197.1
Balance, common stock held in treasury (in shares) at Sep. 30, 2019	14,469,456		14,500,000
Balance, common stock shares issued (in shares) at Jun. 30, 2019		253,200,000
Beginning balance at Jun. 30, 2019	$ 5,288.3	$ 2,703.5	$ (568.4)	(22.3)	3,175.5
Balance, common stock held in treasury (in shares) at Jun. 30, 2019			15,200,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	108.9				108.9
Other comprehensive income (loss)	0.0
Proceeds from sales of common stock through employee equity incentive plans (shares)		900,000
Proceeds from sales of common stock through employee equity incentive plans	20.2	$ 20.2
Restricted stock unit and stock appreciation right withholdings (shares)		(200,000)
Restricted stock unit and stock appreciation right withholdings	(15.2)	$ (15.2)
Treasury stock used for new issuances (shares)		(700,000)	(700,000)
Treasury stock used for new issuances		$ (23.2)	$ 23.2
Share-based compensation	46.4	$ 46.4
Cash dividend	$ (87.3)				(87.3)
Balance, common stock shares issued (in shares) at Sep. 30, 2019	253,232,909	253,200,000
Ending balance at Sep. 30, 2019	$ 5,361.3	$ 2,731.7	$ (545.2)	$ (22.3)	$ 3,197.1
Balance, common stock held in treasury (in shares) at Sep. 30, 2019	14,469,456		14,500,000