Net Sales (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 1,337.8	$ 1,432.5	$ 2,660.4	$ 2,644.9
Payment terms			30 days
Distributors
Disaggregation of Revenue [Line Items]
Net sales	666.1	712.4	$ 1,331.2	1,358.0
Direct customers
Disaggregation of Revenue [Line Items]
Net sales	648.5	681.9	1,287.4	1,222.0
Licensees
Disaggregation of Revenue [Line Items]
Net sales	23.2	38.2	41.8	64.9
Microcontrollers
Disaggregation of Revenue [Line Items]
Net sales	697.8	778.6	1,406.1	1,500.9
Analog, interface, mixed signal and timing products
Disaggregation of Revenue [Line Items]
Net sales	393.9	419.2	780.3	751.1
Field-programmable gate array products
Disaggregation of Revenue [Line Items]
Net sales	93.2	70.8	184.2	108.7
Licensing, memory and other
Disaggregation of Revenue [Line Items]
Net sales	$ 152.9	$ 163.9	$ 289.8	$ 284.2