CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 255.4	$ 164.6	$ 323.9
Net loss attributable to noncontrolling interests	0.0	0.0	0.2
Net income attributable to Microchip Technology	255.4	164.6	324.1
Available-for-sale securities:
Unrealized holding losses, net of tax effect	(13.6)	(1.5)	(3.2)
Reclassification of realized transactions, net of tax effect	15.2	1.5	(10.9)
Defined benefit plans:
Actuarial losses related to defined benefit pension plans, net of tax benefit of $2.4, $2.2, and $0	(5.6)	(5.3)	0.0
Reclassification of realized transactions, net of tax effect	0.8	0.0	0.0
Change in net foreign currency translation adjustment	0.0	(5.7)	0.0
Other comprehensive loss, net of tax effect	(3.2)	(11.0)	(14.1)
Other comprehensive loss attributable to noncontrolling interests	0.0	0.0	0.0
Net other comprehensive loss	(3.2)	(11.0)	(14.1)
Comprehensive income	252.2	153.6	309.8
Less: Comprehensive loss attributable to noncontrolling interests	0.0	0.0	0.2
Comprehensive income attributable to Microchip Technology	$ 252.2	$ 153.6	$ 310.0