Net Sales (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net sales	$ 1,374.7	$ 994.2	$ 4,019.7	$ 2,978.5
Distributors
Disaggregation of Revenue [Line Items]
Net sales	686.3		2,044.4
Direct customers
Disaggregation of Revenue [Line Items]
Net sales	645.0		1,867.0
Licensees
Disaggregation of Revenue [Line Items]
Net sales	43.4		108.3
Microcontrollers
Disaggregation of Revenue [Line Items]
Net sales	716.9		2,218.0
Analog, interface, mixed signal and timing products
Disaggregation of Revenue [Line Items]
Net sales	396.6		1,147.7
Memory products
Disaggregation of Revenue [Line Items]
Net sales	44.0		142.0
Field-programmable gate array products
Disaggregation of Revenue [Line Items]
Net sales	97.7		206.4
Technology licensing
Disaggregation of Revenue [Line Items]
Net sales	43.4		108.3
Multi-market and other
Disaggregation of Revenue [Line Items]
Net sales	$ 76.1		$ 197.3