EARNINGS PER SHARE - Computation of Net Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 28, 2018	Dec. 29, 2017
Earnings Per Share [Abstract]
Net earnings (loss)	$ 103.9	$ (112.2)
Less: Net earnings attributable to noncontrolling interests	0.7	0.1
Net earnings (loss) attributable to Varian	$ 103.2	$ (112.3)
Weighted average shares outstanding - basic (in shares)	91.0	91.6
Dilutive effect of potential common shares (in shares)	1.0	0.0
Weighted average shares outstanding - diluted (in shares)	92.0	91.6
Net earnings (loss) per share attributable to Varian - basic (in dollars per share)	$ 1.13	$ (1.22)
Net earnings (loss) per share attributable to Varian - diluted (in dollars per share)	$ 1.12	$ (1.22)
Anti-dilutive employee shared based awards, excluded (in shares)	0.9	3.2