Business Acquisitions - Schedule of Purchase Price Allocation, Atmel (Details) - USD ($) $ in Millions	Mar. 31, 2019	Mar. 31, 2018	Apr. 04, 2016
Business Acquisition [Line Items]
Goodwill	$ 6,663.9	$ 2,299.0
Atmel Corporation
Business Acquisition [Line Items]
Cash and cash equivalents			$ 230.2
Accounts receivable			141.4
Inventories			335.1
Prepaid expenses and other current assets			28.4
Assets held for sale			32.0
Property, plant and equipment			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)
Deferred tax liabilities			(27.5)
Long-term income tax payable			(115.1)
Other long-term liabilities			(141.7)
Total liabilities assumed			(653.0)
Purchase price allocated			$ 3,473.0