Comprehensive Income (Schedule Of Reclassifications Of Recognized Transactions Out Of AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (loss) income, net	$ (5.8)	$ 1.3	$ 8.9
Income tax provision	(481.9)	80.8	42.6
Net income attributable to Microchip Technology	255.4	164.6	324.1
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Unrealized Investment Gain (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (loss) income, net	(15.5)	(1.5)	10.9
Income tax provision	0.3	0.0	0.0
Net income attributable to Microchip Technology	(16.0)	(1.5)	10.9
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Defined Benefit Plans Adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other (loss) income, net	$ (0.8)	$ 0.0	$ 0.0