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		6 Months Ended
	Mar. 29, 2019	Mar. 30, 2018	Mar. 29, 2019	Mar. 30, 2018
Earnings Per Share [Abstract]
Net earnings (loss)	$ 88.4	$ 73.2	$ 192.3	$ (39.0)
Less: Net earnings (loss) attributable to noncontrolling interests	(0.2)	0.0	0.5	0.1
Net earnings (loss) attributable to Varian	$ 88.6	$ 73.2	$ 191.8	$ (39.1)
Weighted average shares outstanding - basic (in shares)	91.0	91.5	91.0	91.6
Dilutive effect of potential common shares (in shares)	0.9	1.1	1.0	0.0
Weighted average shares outstanding - diluted (in shares)	91.9	92.6	92.0	91.6
Net earnings (loss) per share attributable to Varian - basic (in dollars per share)	$ 0.97	$ 0.80	$ 2.11	$ (0.43)
Net earnings (loss) per share attributable to Varian - diluted (in dollars per share)	$ 0.96	$ 0.79	$ 2.09	$ (0.43)
Anti-dilutive employee shared based awards, excluded (in shares)	0.5	0.6	1.0	3.2