Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 1,002.3	$ 994.2	$ 1,012.1	$ 972.1	$ 902.7	$ 834.4	$ 871.4	$ 799.4	$ 3,980.8	$ 3,407.8	$ 2,173.3
Gross profit	615.1	607.1	614.1	584.4	532.8	465.3	410.6	348.5	2,420.7	1,757.2	1,205.5
Operating income	244.1	245.2	225.4	221.6	154.1	118.1	62.8	(59.1)	936.3	275.8	352.3
Net income from continuing operations	$ 146.7	$ (251.1)	$ 189.2	$ 170.6	$ 136.9	$ 107.2	$ 33.9	$ (113.4)	$ 255.4	$ 164.6	$ 323.9
Net income attributable to Microchip Technology (in usd per share)	$ 0.58	$ (1.07)	$ 0.77	$ 0.70	$ 0.57	$ 0.46	$ 0.14	$ (0.53)	$ 1.03	$ 0.71	$ 1.49
Loss on settlement of convertible debt		$ 2.2		$ 13.8	$ 43.9				$ 16.0	$ 43.9	$ 0.0	$ 50.6