Significant Accounting Policies - Topic 606 (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	Apr. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales										$ 5,349.5	$ 3,980.8	$ 3,407.8
Cost of sales	[1]									2,418.2	1,560.1	1,650.6
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
Income before income taxes										204.5	737.3	89.8
Income tax (benefit) provision										(151.4)	481.9	(80.8)
Net income from continuing operations		174.7	$ 49.2	$ 96.3	$ 35.7	146.7	$ (251.1)	$ 189.2	$ 170.6	355.9	255.4	$ 170.6
Accounts receivable, net		880.6				563.7				880.6	563.7		$ 903.8
Inventories		711.7				476.2				711.7	476.2		471.1
Other current assets		191.6				119.8				191.6	119.8		137.0
Other assets		111.8				71.8				111.8	71.8		47.7
Long-term deferred tax assets		1,677.2				100.2				1,677.2	100.2		1,656.5
Accrued liabilities		787.3				229.6				787.3	229.6		633.8
Deferred income on shipments to distributors		0.0				333.8				0.0	333.8		0.0
Long-term deferred tax liability		706.1				205.8				706.1	205.8		221.5
Retained earnings		3,210.6				1,397.3				3,210.6	1,397.3		$ 3,199.0
Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net						340.1					340.1
Inventories						(5.1)					(5.1)
Other current assets						17.2					17.2
Other assets						0.0					0.0
Long-term deferred tax assets						(23.1)					(23.1)
Accrued liabilities						404.2					404.2
Deferred income on shipments to distributors						(333.8)					(333.8)
Long-term deferred tax liability						16.8					16.8
Retained earnings						$ 241.9					$ 241.9
Calculated under Revenue Guidance in Effect before Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales										5,380.1
Cost of sales										2,434.0
Gross profit										2,946.1
Income before income taxes										219.3
Income tax (benefit) provision										(149.0)
Net income from continuing operations										368.3
Accounts receivable, net		556.1								556.1
Inventories		724.2								724.2
Other current assets		154.7								154.7
Other assets		106.3								106.3
Long-term deferred tax assets		1,700.7								1,700.7
Accrued liabilities		420.3								420.3
Deferred income on shipments to distributors		288.2								288.2
Long-term deferred tax liability		689.3								689.3
Retained earnings		2,975.3								2,975.3
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales										(30.6)
Cost of sales										(15.8)
Gross profit										(14.8)
Income before income taxes										(14.8)
Income tax (benefit) provision										(2.4)
Net income from continuing operations										(12.4)
Accounts receivable, net		324.5								324.5
Inventories		(12.5)								(12.5)
Other current assets		36.9								36.9
Other assets		5.5								5.5
Long-term deferred tax assets		(23.5)								(23.5)
Accrued liabilities		367.0								367.0
Deferred income on shipments to distributors		(288.2)								(288.2)
Long-term deferred tax liability		16.8								16.8
Retained earnings		$ 235.3								$ 235.3

[1] (1) Includes share-based compensation expense as follows: Cost of sales$14.9 $13.8 $18.7Research and development$72.0 $42.5 $46.8Selling, general and administrative$62.3 $36.9 $62.6Special charges and other, net$17.2 $— $—