Business Acquisitions (Schedule of Purchase Price Allocation) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Apr. 04, 2016	Aug. 03, 2015
Business Acquisition [Line Items]
Goodwill	$ 2,299.0	$ 2,299.0
Atmel Corporation
Business Acquisition [Line Items]
Cash and cash equivalents			$ 230.2
Accounts receivable, net			141.4
Inventories			335.1
Prepaid expenses and other current assets			28.4
Assets held for sale			32.0
Property, plant and equipment, net			129.9
Goodwill			1,286.4
Purchased intangible assets			1,888.4
Long-term deferred tax assets			46.7
Other assets			7.5
Total assets acquired			4,126.0
Accounts payable			(55.7)
Other current liabilities			(121.0)
Long-term line of credit			(192.0)
Long-term income tax payable			(115.1)
Deferred tax liabilities			(27.5)
Other long-term liabilities			(141.7)
Total liabilities assumed			(653.0)
Purchase price allocated			$ 3,473.0
Micrel Incorporated
Business Acquisition [Line Items]
Cash and cash equivalents				$ 99.1
Accounts receivable, net				14.0
Inventories				73.5
Prepaid expenses and other current assets				10.7
Property, plant and equipment, net				38.5
Goodwill				441.0
Purchased intangible assets				273.5
Long-term deferred tax assets				11.4
Other assets				4.3
Total assets acquired				954.6
Accounts payable				(11.1)
Other current liabilities				(31.6)
Long-term income tax payable				(7.6)
Deferred tax liabilities				(88.0)
Other long-term liabilities				(0.1)
Total liabilities assumed				(138.4)
Purchase price allocated				$ 816.2