Segment and Related Information - Schedule of Total Operating Income for Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting [Abstract]
Total operating income for reportable segments	$ (20.9)	$ 1.2
Interest income	0.9	0.7
Interest expense	(2.9)	(2.2)
Other	0.6	1.1
Income (loss) before income tax	(22.3)	0.8
Income tax provision (benefit)	(1.7)	1.6
Net income (loss)	(20.6)	(0.8)
Net loss attributable to non-controlling interest		(0.1)
Net income (loss) attributable to Myriad Genetics, Inc. stockholders	$ (20.6)	$ (0.7)