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								12 Months Ended
	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 30, 2016	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net earnings from continuing operations	$ 116.8	$ 72.5	$ 73.2	$ (112.2)	$ 78.6	$ 69.9	$ 69.5	$ 8.0	$ 150.3	$ 226.0	$ 322.3
Less: Net earnings (loss) from continuing operations attributable to noncontrolling interests									0.4	0.6	(0.1)
Net earnings from continuing operations attributable to Varian									149.9	225.4	322.4
Net (loss) earnings from discontinued operations					0.0	0.0	(13.3)	6.5	0.0	(6.8)	77.4
Less: Net earnings from discontinued operations attributable to noncontrolling interests									0.0	0.1	0.5
Net earnings (loss) from discontinued operations attributable to Varian									0.0	(6.9)	76.9
Net (loss) earnings attributable to Varian	$ 116.4	$ 72.6	$ 73.2	$ (112.3)	$ 78.6	$ 69.7	$ 56.3	$ 13.9	$ 149.9	$ 218.5	$ 399.3
Weighted average shares outstanding - basic (in shares)									91.5	92.5	95.4
Dilutive effect of potential common shares (in shares)									1.0	0.7	0.6
Weighted average shares outstanding - diluted (in shares)									92.5	93.2	96.0
Net earnings (loss) per share from continuing operations - basic (in dollars per share)					$ 0.86	$ 0.76	$ 0.75	$ 0.08	$ 1.64	$ 2.44	$ 3.38
Net earnings (loss) per share from discontinued operations - basic (in dollars per share)					0.00	0.00	(0.15)	0.07	0.00	(0.08)	0.81
Net earnings per share - basic (in dollars per share)	$ 1.27	$ 0.79	$ 0.80	$ (1.22)	0.86	0.76	0.60	0.15	1.64	2.36	4.19
Net earnings (loss) per share from continuing operations - diluted (in dollars per share)					0.85	0.75	0.74	0.08	1.62	2.42	3.36
Net earnings (loss) per share from discontinued operations - diluted (in dollars per share)					0.00	0.00	(0.14)	0.07	0.00	(0.07)	0.80
Net earnings per share - diluted (in dollars per share)	$ 1.26	$ 0.79	$ 0.79	$ (1.22)	$ 0.85	$ 0.75	$ 0.60	$ 0.15	$ 1.62	$ 2.35	$ 4.16
Anti-dilutive employee shared based awards, excluded (in shares)									0.7	0.2	1.6