Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,644.1		$ 2,644.1	$ 2,452.3
Less accumulated depreciation and amortization	1,876.2		1,876.2	1,769.0
Total property, plant and equipment, net	767.9		767.9	683.3
Depreciation			123.7	122.9	$ 103.9
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	73.4		73.4	73.4
Building and Building Improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	508.5		508.5	499.7
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,943.9		1,943.9	1,774.9
Construction in Progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	118.3		$ 118.3	$ 104.3
Building
Property, Plant and Equipment [Line Items]
Purchase of building	$ 40.8
Micrel Incorporated
Property, Plant and Equipment [Line Items]
Proceeds from sale of property and assets		$ 10.0