Geographic and Segment Information - Gross Profit (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net sales	$ 1,329.8	$ 1,374.7	$ 1,432.5	$ 1,212.5	$ 1,002.3	$ 994.2	$ 1,012.1	$ 972.1	$ 5,349.5	$ 3,980.8	$ 3,407.8
Gross profit	$ 820.5	$ 779.6	$ 689.3	$ 642.0	$ 615.1	$ 607.1	$ 614.1	$ 584.4	2,931.3	2,420.7	1,757.2
Semiconductor Products Reporting Unit
Segment Reporting Information [Line Items]
Net sales									5,217.1	3,876.0	3,316.6
Gross profit									2,798.9	2,315.9	1,666.0
Technology Licensing Reporting Unit
Segment Reporting Information [Line Items]
Net sales									132.4	104.8	91.2
Gross profit									$ 132.4	$ 104.8	$ 91.2