Net Income Per Common Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income	$ 49.2	$ (251.1)	$ 181.2	$ 108.7
Basic common shares outstanding (in shares)	236,700,000	234,100,000	235,900,000	232,300,000
Dilutive effect of stock options and RSUs (in shares)	3,300,000	0	3,800,000	4,400,000
Weighted average common and potential common shares outstanding (in shares)	244,600,000	234,100,000	249,500,000	248,000,000
Basic net income attributable to Microchip Technology, per common share (in usd per share)	$ 0.21	$ (1.07)	$ 0.77	$ 0.47
Incremental common shares attributable to dilutive effect of written put options (in shares)	0	4,400,000	0	0
Diluted net income attributable to Microchip Technology, per common share (in usd per share)	$ 0.20	$ (1.07)	$ 0.73	$ 0.44
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 (in shares)	0	0	0	1,700,000
Incremental common shares attributable to dilutive effect of written put options (in shares)		400,000
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (in usd per share)	$ 0.00	$ 23.49	$ 0.00	$ 23.59
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 (in shares)	4,600,000	0	9,800,000	9,600,000
Incremental common shares attributable to dilutive effect of written put options (in shares)		11,900,000
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (in usd per share)	$ 62.72	$ 63.80	$ 63.00	$ 64.07
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 (in shares)	0	0	0	0
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (in usd per share)	$ 97.81	$ 99.50	$ 98.25	$ 99.92
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 (in shares)	0	0	0	0
Weighted average conversion price per share used in calculating dilutive effect of convertible debt (in usd per share)	$ 96.10	$ 97.75	$ 96.53	$ 98.16