Net Sales (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 1,287.4	$ 1,374.7	$ 3,947.8	$ 4,019.7
Payment terms			30 days
Distributors
Disaggregation of Revenue [Line Items]
Net sales	638.8	686.3	$ 1,970.0	2,044.4
Direct customers
Disaggregation of Revenue [Line Items]
Net sales	618.2	645.0	1,905.6	1,867.0
Licensees
Disaggregation of Revenue [Line Items]
Net sales	30.4	43.4	72.2	108.3
Microcontrollers
Disaggregation of Revenue [Line Items]
Net sales	685.8	716.9	2,091.8	2,218.0
Analog, interface, mixed signal and timing products
Disaggregation of Revenue [Line Items]
Net sales	363.3	396.6	1,143.6	1,147.7
Field-programmable gate array products
Disaggregation of Revenue [Line Items]
Net sales	92.6	97.7	276.8	206.4
Licensing, memory and other
Disaggregation of Revenue [Line Items]
Net sales	$ 145.7	$ 163.5	$ 435.6	$ 447.6