Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Oct. 02, 2020	Jul. 03, 2020	Apr. 03, 2020	Jan. 03, 2020	Sep. 27, 2019	Jun. 28, 2019	Mar. 29, 2019	Dec. 28, 2018	Oct. 02, 2020	Sep. 27, 2019	Sep. 28, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 850.5	$ 694.3	$ 794.5	$ 828.9	$ 878.9	$ 825.8	$ 779.4	$ 741.0	$ 3,168.2	$ 3,225.1	$ 2,919.1
Gross margin	374.7	298.5	337.2	366.8	384.6	351.4	318.2	316.1	1,377.2	1,370.3	1,273.6
Net earnings (loss)	76.5	60.9	43.1	88.9	70.4	29.5	88.4	103.9	269.4	292.2	150.3
Net earnings attributable to Varian	$ 76.6	$ 61.2	$ 43.2	$ 88.2	$ 70.7	$ 29.4	$ 88.6	$ 103.2	$ 269.2	$ 291.9	$ 149.9
Net earnings per share - basic (in dollars per share)	$ 0.84	$ 0.67	$ 0.48	$ 0.97	$ 0.78	$ 0.32	$ 0.97	$ 1.13	$ 2.96	$ 3.21	$ 1.64
Net earnings per share - diluted (in dollars per share)	$ 0.83	$ 0.67	$ 0.47	$ 0.96	$ 0.77	$ 0.32	$ 0.96	$ 1.12	$ 2.94	$ 3.18	$ 1.62
Gain on investments	$ 14.8	$ 25.7
Litigation charges and legal costs	10.9
Restructuring charges		13.9							$ 18.7
Available for sale securities, impairment charge	8.6	9.2
Impairment charges			$ 40.5						58.3	$ 50.6	$ 22.4
Change in amount of contingent consideration	$ 18.6		$ 8.9	$ 8.8				$ 11.6	(0.3)	18.6	0.0
Gain on sale of investment				$ 22.0					41.5	23.8	0.0
Goodwill impairment charge		50.5								50.5
Write-off of in-process research and development related to acquisition-related activities		$ 20.8							$ 0.0	$ 20.8	$ 0.0