Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss) attributable to Myriad Genetics, Inc. stockholders	$ (115.2)	$ 6.9	$ (144.1)	$ 8.8
Unrealized gain (loss) on available-for-sale debt securities, net of tax	(0.1)	0.3	(0.1)	0.7
Change in foreign currency translation adjustment, net of tax	(2.5)	(1.0)	(2.4)	(2.3)
Comprehensive income (loss)	(117.8)	6.2	(146.6)	7.2
Comprehensive income attributable to non-controlling interest	0.0	0.0	0.0	0.0
Comprehensive income (loss) attributable to Myriad Genetics, Inc. shareholders	$ (117.8)	$ 6.2	$ (146.6)	$ 7.2