CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions		3 Months Ended			6 Months Ended
		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales		$ 1,432.5	$ 1,012.1		$ 2,644.9	$ 1,984.3
Cost of sales		743.2	398.0	[1]	1,313.6	785.8	[1]
Gross profit		689.3	614.1		1,331.3	1,198.5
Research and development	[1]	221.9	133.6		393.8	264.0
Selling, general and administrative	[1]	176.6	114.3		340.7	228.6
Amortization of acquired intangible assets		169.9	120.9		303.6	241.8
Special charges and other, net	[1]	18.2	19.9		58.3	17.1
Operating expenses		586.6	388.7		1,096.4	751.5
Operating income		102.7	225.4		234.9	447.0
Losses on equity method investment		(0.1)	(0.1)		(0.1)	(0.1)
Other income (expense):
Interest income		0.9	4.6		6.6	8.1
Interest expense		(138.6)	(49.5)		(229.0)	(98.9)
Loss on settlement of debt		(4.1)	0.0		(4.1)	(13.8)
Other (loss) income, net		(0.2)	5.8		(10.0)	10.1
(Loss) income before income taxes		(39.4)	186.2		(1.7)	352.4
Income tax benefit		(135.7)	(3.0)		(133.7)	(7.3)
Net income		$ 96.3	$ 189.2		$ 132.0	$ 359.7
Basic net income attributable to Microchip Technology, per common share (in usd per share)		$ 0.41	$ 0.81		$ 0.56	$ 1.55
Diluted net income attributable to Microchip Technology, per common share (in usd per share)		0.38	0.77		0.52	1.48
Dividends declared per common share (in usd per share)		$ 0.364	$ 0.362		$ 0.7275	$ 0.7235
Basic common shares outstanding (in shares)		235.8	233.3		235.5	231.4
Diluted common shares outstanding (in shares)		251.8	244.8		252.0	243.8

[1] (1) Includes share-based compensation expense as follows: Cost of sales$3.9 $3.7 $7.5 $7.1Research and development$19.7 $10.6 $33.8 $20.9Selling, general and administrative$17.8 $9.3 $29.5 $18.0Special charges and other, net$1.2 $— $17.1 $—