Net Sales (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Net sales	$ 5,349.5	$ 3,980.8	$ 3,407.8
Distributors
Disaggregation of Revenue [Line Items]
Net sales	2,719.1
Direct customers
Disaggregation of Revenue [Line Items]
Net sales	2,498.0
Licensees
Disaggregation of Revenue [Line Items]
Net sales	132.4
Microcontrollers
Disaggregation of Revenue [Line Items]
Net sales	2,921.9
Analog, interface, mixed signal and timing products
Disaggregation of Revenue [Line Items]
Net sales	1,530.7
Field-programmable gate array products
Disaggregation of Revenue [Line Items]
Net sales	303.8
Memory products
Disaggregation of Revenue [Line Items]
Net sales	184.0
Technology licensing
Disaggregation of Revenue [Line Items]
Net sales	132.4
Multi-market and other
Disaggregation of Revenue [Line Items]
Net sales	$ 276.7