Intangible Assets and Goodwill - Intangible Assets (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	May 29, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount		$ 8,151.5		$ 8,151.5		$ 2,683.1
Accumulated Amortization		(1,518.6)		(1,518.6)		(1,021.1)
Net Amount		6,632.9		6,632.9		1,662.0
In-process technology reaching technological feasibility and reclassified				798.6
Amortization of intangible assets		196.9	$ 122.6	505.5	$ 368.1
Impairment of intangible assets				3.1	0.3
Projected Amortization Expense
2019		196.8		196.8
2020		992.0		992.0
2021		926.7		926.7
2022		851.8		851.8
2023		660.5		660.5
Core and developed technology
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount		7,064.4		7,064.4		1,952.3
Accumulated Amortization		(984.5)		(984.5)		(644.4)
Net Amount		6,079.9		6,079.9		1,307.9
Customer-related
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount		1,043.8		1,043.8		716.9
Accumulated Amortization		(512.3)		(512.3)		(375.9)
Net Amount		531.5		531.5		341.0
Backlog
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount		27.9		27.9
Accumulated Amortization		(19.5)		(19.5)
Net Amount		8.4		8.4
In-process research and development
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount		7.7		7.7		12.1
Accumulated Amortization		0.0		0.0		0.0
Net Amount		7.7		7.7		12.1
Distribution rights
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount		0.3		0.3		0.3
Accumulated Amortization		(0.2)		(0.2)		(0.1)
Net Amount		0.1		0.1		0.2
Other
Finite-Lived Intangible Assets, Net [Abstract]
Gross Amount		7.4		7.4		1.5
Accumulated Amortization		(2.1)		(2.1)		(0.7)
Net Amount		5.3		$ 5.3		$ 0.8
Minimum
Finite-Lived Intangible Assets, Net [Abstract]
Useful life (in years)				1 year
Maximum
Finite-Lived Intangible Assets, Net [Abstract]
Useful life (in years)				15 years
Microsemi Corporation
Finite-Lived Intangible Assets, Net [Abstract]
Useful life (in years)	9 years
Purchased intangible assets	$ 5,466.9
Microsemi Corporation | Core and developed technology
Finite-Lived Intangible Assets, Net [Abstract]
Useful life (in years)	15 years			15 years
Purchased intangible assets	$ 4,312.1			$ 4,310.0
Microsemi Corporation | Customer-related
Finite-Lived Intangible Assets, Net [Abstract]
Useful life (in years)				12 years
Purchased intangible assets				$ 326.9
Microsemi Corporation | Backlog
Finite-Lived Intangible Assets, Net [Abstract]
Useful life (in years)	1 year			1 year
Purchased intangible assets	$ 27.9			$ 27.9
Microsemi Corporation | In-process research and development
Finite-Lived Intangible Assets, Net [Abstract]
Purchased intangible assets		794.2
Microsemi Corporation | Other
Finite-Lived Intangible Assets, Net [Abstract]
Useful life (in years)	4 years			4 years
Purchased intangible assets	$ 5.8			$ 5.8
Cost of sales
Finite-Lived Intangible Assets, Net [Abstract]
Amortization of intangible assets		1.8	1.5	4.9	4.9
Operating expense
Finite-Lived Intangible Assets, Net [Abstract]
Amortization of intangible assets		$ 195.1	$ 121.1	$ 500.6	$ 363.2