Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 96.3	$ 189.2	$ 132.0	$ 359.7
Weighted average common shares outstanding	235,800,000	233,300,000	235,500,000	231,400,000
Dilutive effect of stock options and RSUs	4,300,000	4,500,000	4,200,000	4,400,000
Incremental common shares attributable to dilutive effect of written put options	0	0	0	0
Weighted average common and potential common shares outstanding	251,800,000	244,800,000	252,000,000	243,800,000
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
2007 Junior Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Incremental common shares attributable to dilutive effect of conversion of debt securities	0	700,000	0	2,400,000
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$ 0.00	$ 23.58	$ 0.00	$ 23.64
2015 Senior Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Incremental common shares attributable to dilutive effect of conversion of debt securities	11,700,000	6,300,000	12,300,000	5,600,000
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$ 63.02	$ 64.06	$ 63.14	$ 64.21
2017 Senior Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Incremental common shares attributable to dilutive effect of conversion of debt securities	0	0	0	0
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$ 98.27	$ 99.90	$ 98.47	$ 100.13
2017 Junior Convertible Debt
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Incremental common shares attributable to dilutive effect of conversion of debt securities	0	0	0	0
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (amount per share)	$ 96.55	$ 98.15	$ 96.74	$ 98.37