Goodwill by Reporting Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Apr. 04, 2016
Goodwill [Roll Forward]
Goodwill, ending balance	$ 2,299.0
Goodwill	2,299.0	$ 2,299.0
Atmel Corporation
Goodwill [Roll Forward]
Goodwill			$ 1,286.4
Semiconductor products
Goodwill [Roll Forward]
Goodwill, beginning balance	993.5
Goodwill, ending balance	2,279.8
Goodwill	993.5	2,279.8
Semiconductor products | Atmel Corporation
Goodwill [Roll Forward]
Additions due to business combination	1,286.3
Technology licensing
Goodwill [Roll Forward]
Goodwill, beginning balance	19.2
Goodwill, ending balance	19.2
Goodwill	19.2	$ 19.2
Technology licensing | Atmel Corporation
Goodwill [Roll Forward]
Additions due to business combination	$ 0.0