Special Charges and Other, Net - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Restructuring Cost and Reserve [Line Items]
Supply Commitment, Period		10 years
Non-restructuring contract exit costs and other		$ 0.0	$ 20.0	$ 0.0
Employee separation costs		65.3	1.2	39.1
Contract exit costs		(4.7)	0.7	44.1
Gain on sale of assets		0.0	4.4	0.0
Contract Termination
Restructuring Cost and Reserve [Line Items]
Non-restructuring contract exit costs and other			$ 19.5
Contract termination fee, period			5 years
Atmel Corporation
Restructuring Cost and Reserve [Line Items]
Employee separation costs			$ 1.2
Semiconductor Products | Contract Termination
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, cost incurred to date		40.8
Contract exit costs		(4.7)	$ 0.7	$ 44.1
Semiconductor Products | Employee Separation
Restructuring Cost and Reserve [Line Items]
Employee separation costs		65.3
Restructuring and related cost, cost incurred to date		$ 115.2
San Jose Facility | Micrel Incorporated
Restructuring Cost and Reserve [Line Items]
Proceeds from sale of property and assets	$ 10.0
Gain on sale of assets	$ 4.4