Net Sales (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total net sales	$ 1,309.5	$ 1,337.8	$ 2,619.2	$ 2,660.4
Distributors
Disaggregation of Revenue [Line Items]
Total net sales	663.2	666.1	1,322.1	1,331.2
Direct customers
Disaggregation of Revenue [Line Items]
Total net sales	623.0	648.5	1,251.9	1,287.4
Licensees
Disaggregation of Revenue [Line Items]
Total net sales	23.3	23.2	45.2	41.8
Microcontrollers
Disaggregation of Revenue [Line Items]
Total net sales	703.1	697.8	1,419.5	1,406.1
Analog
Disaggregation of Revenue [Line Items]
Total net sales	361.7	393.9	731.9	780.3
FPGA
Disaggregation of Revenue [Line Items]
Total net sales	108.4	93.2	195.2	184.2
LMO
Disaggregation of Revenue [Line Items]
Total net sales	$ 136.3	$ 152.9	$ 272.6	$ 289.8