Net income per common share attributable to Microchip Technology Stockholders (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				12 Months Ended
	Nov. 30, 2017	Jun. 30, 2017	Feb. 28, 2017	Feb. 28, 2015	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income from continuing operations attributable to Microchip Technology Stockholders					$ 255.4	$ 170.6	$ 324.1
Weighted average common shares outstanding					232,900,000	217,200,000	203,400,000
Dilutive effect of stock options and RSUs					4,400,000	4,400,000	3,300,000
Weighted average common and potential common shares outstanding					248,900,000	234,800,000	217,400,000
Net income from continuing operations (in usd per share)					$ 1.10	$ 0.79	$ 1.59
Net income from continuing operations (in usd per share)					$ 1.03	$ 0.73	$ 1.49
Number of antidilutive option shares (in shares)					0	0	298,015
2007 Junior Subordinated Convertible Notes
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of subordinated convertible debentures					1,300,000	12,700,000	10,700,000
Shares issued to settle convertible debt					3,700,000
Extinguishment of debt, amount					$ 143.8
Weighted average conversion price per share used in calculating dilutive effect of convertible debt amount per share					$ 23.59	$ 24.01	$ 24.73
2015 Senior Subordinated Convertible Debt
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of subordinated convertible debentures					10,300,000	500,000	0
Weighted average conversion price per share used in calculating dilutive effect of convertible debt amount per share					$ 63.94	$ 65.21	$ 67.19
2017 Senior Subordinated Convertible Debt
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of subordinated convertible debentures					0	0	0
Weighted average conversion price per share used in calculating dilutive effect of convertible debt amount per share					$ 99.71	$ 100.58	$ 0.00
2017 Junior Subordinated Convertible Debt
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of subordinated convertible debentures					0	0	0
Weighted average conversion price per share used in calculating dilutive effect of convertible debt amount per share					$ 97.96	$ 98.81	$ 0.00
Long-term Debt | 2007 Junior Subordinated Convertible Notes
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued to settle convertible debt		3,200,000	11,997,924		3,200,000
Extinguishment of debt, amount	$ 14.6	$ 111.3	$ 431.3	$ 575.0	$ 111.3