Special (Income) Charges and Other, Net - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Employee separation costs	$ 3.3	$ 0.1			$ 60.5	$ 1.5
Contract exit costs	0.1	(0.1)			(2.9)	0.6
Non-restructuring contract exit costs and other	$ 0.0	0.1			0.0	19.6
Supply commitment, period	10 years
Gain on sale of assets	$ 0.0	$ 0.0			0.0	$ 4.4
Restructuring reserve	$ 51.5				51.5		$ 47.2
Contract termination
Restructuring Cost and Reserve [Line Items]
Non-restructuring contract exit costs and other			$ 19.5
Contract termination fee, period	5 years
Employee Separation Costs
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 13.5				13.5		$ 0.8
Semiconductor products
Restructuring Cost and Reserve [Line Items]
Employee separation costs	3.3
Contract exit costs	0.1
Semiconductor products | Contract termination
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred to date	42.6				42.6
Semiconductor products | Employee Separation Costs
Restructuring Cost and Reserve [Line Items]
Restructuring costs incurred to date	$ 110.4				$ 110.4
Micrel Incorporated
Restructuring Cost and Reserve [Line Items]
Proceeds from sale of property, plant, and equipment				$ 10.0
San Jose Facility | Micrel Incorporated
Restructuring Cost and Reserve [Line Items]
Gain on sale of assets				$ 4.4