Intangible Assets and Goodwill - Goodwill by Reporting Segment (Details) $ in Millions	6 Months Ended
Sep. 30, 2019 USD ($) unit
Goodwill By Reporting Segment [Line Items]
Number of reporting units (in units) \| unit	2
Goodwill [Roll Forward]
Goodwill opening balance	$ 6,663.9
Goodwill closing balance	6,664.6
Semiconductor Products Reporting Unit
Goodwill [Roll Forward]
Goodwill opening balance	6,644.7
Additions	0.7
Goodwill closing balance	6,645.4
Technology Licensing Reporting Unit
Goodwill [Roll Forward]
Goodwill opening balance	19.2
Additions	0.0
Goodwill closing balance	$ 19.2

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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Number of reporting units tested for impairment of goodwill. A reporting unit is an operating segment or one level below an operating segment.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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