Segment Information - Reconciliation of Segment Operating Results to Companys Earnings from Continuing Operations before Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 29, 2017	Sep. 30, 2016	Oct. 02, 2015
Segment Reporting Information [Line Items]
Operating Earnings	$ 341.9	$ 435.0	$ 395.7
Interest income, net	2.9	5.6	5.6
Total earnings from continuing operations before taxes	344.8	440.6	401.3
Corporate
Segment Reporting Information [Line Items]
Operating Earnings	(83.1)	(33.4)	(19.0)
Operating Segments | Oncology Systems
Segment Reporting Information [Line Items]
Operating Earnings	520.7	518.6	447.4
Operating Segments | Varian Particle Therapy
Segment Reporting Information [Line Items]
Operating Earnings	(95.7)	(44.6)	(26.5)
Operating Segments | Total reportable segments
Segment Reporting Information [Line Items]
Operating Earnings	425.0	474.0	420.9
Operating Segments | Other
Segment Reporting Information [Line Items]
Operating Earnings	0.0	(5.6)	(6.2)
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Operating Earnings	$ (83.1)	$ (33.4)	$ (19.0)