Segment Information - Operating Results Information for Each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 30, 2016	Sep. 30, 2016	Jul. 01, 2016	Apr. 01, 2016	Jan. 01, 2016	Sep. 29, 2017	Sep. 30, 2016	Oct. 02, 2015
Segment Reporting Information [Line Items]
Revenues	$ 739.0	$ 662.4	$ 655.0	$ 611.8	$ 747.2	$ 642.9	$ 615.2	$ 615.8	$ 2,668.2	$ 2,621.1	$ 2,490.7
Operating Earnings									341.9	435.0	395.7
Depreciation & Amortization									76.9	79.8	68.5
Total Assets	3,179.4				3,814.8				3,179.4	3,814.8	3,578.7
Discontinued Operations
Segment Reporting Information [Line Items]
Depreciation & Amortization									6.6	16.0	13.2
Total Assets	11.1				628.5				11.1	628.5	595.3
Corporate
Segment Reporting Information [Line Items]
Operating Earnings									(83.1)	(33.4)	(19.0)
Depreciation & Amortization									24.8	28.3	28.5
Total Assets	1,361.2				1,325.2				1,361.2	1,325.2	1,275.9
Operating Segments | Oncology Systems
Segment Reporting Information [Line Items]
Revenues									2,485.7	2,458.0	2,346.8
Operating Earnings									520.7	518.6	447.4
Depreciation & Amortization									39.4	28.5	21.8
Total Assets	1,452.7				1,491.2				1,452.7	1,491.2	1,411.3
Operating Segments | Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues									182.5	162.6	143.5
Operating Earnings									(95.7)	(44.6)	(26.5)
Depreciation & Amortization									6.1	6.8	4.8
Total Assets	354.4				367.8				354.4	367.8	294.0
Operating Segments | Total reportable segments
Segment Reporting Information [Line Items]
Revenues									2,668.2	2,620.6	2,490.3
Operating Earnings									425.0	474.0	420.9
Depreciation & Amortization									45.5	35.3	26.6
Total Assets	1,807.1				1,859.0				1,807.1	1,859.0	1,705.3
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues									0.0	0.5	0.4
Operating Earnings									0.0	(5.6)	(6.2)
Depreciation & Amortization									0.0	0.2	0.2
Total Assets	$ 0.0				$ 2.1				0.0	2.1	2.2
Operating Segments | Corporate
Segment Reporting Information [Line Items]
Operating Earnings									(83.1)	(33.4)	(19.0)
Operating Segments | Product | Oncology Systems
Segment Reporting Information [Line Items]
Revenues									1,383.0	1,430.3	1,359.2
Operating Segments | Product | Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues									172.5	153.1	137.9
Operating Segments | Service | Oncology Systems
Segment Reporting Information [Line Items]
Revenues									1,102.7	1,027.7	987.6
Operating Segments | Service | Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues									$ 10.0	$ 9.5	$ 5.6