SEGMENT INFORMATION - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 29, 2018	Jun. 30, 2017	Jun. 29, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 709.1	$ 632.8	$ 2,117.5	$ 1,897.5
Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	326.9	253.7	1,028.9	870.9
Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	382.2	379.1	1,088.6	1,026.6
Americas
Disaggregation of Revenue [Line Items]
Revenues	342.6	336.3	1,039.5	976.1
EMEA
Disaggregation of Revenue [Line Items]
Revenues	229.7	169.5	676.5	538.8
APAC
Disaggregation of Revenue [Line Items]
Revenues	136.8	127.0	401.5	382.6
North America
Disaggregation of Revenue [Line Items]
Revenues	318.1	324.1	982.3	925.8
International
Disaggregation of Revenue [Line Items]
Revenues	391.0	308.7	1,135.2	971.7
Hardware
Disaggregation of Revenue [Line Items]
Revenues	314.6	281.4	976.7	859.4
Software
Disaggregation of Revenue [Line Items]
Revenues	125.1	110.4	366.9	342.8
Service
Disaggregation of Revenue [Line Items]
Revenues	269.4	241.0	773.9	695.3
Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues	667.2	564.4	2,014.6	1,767.5
Oncology Systems | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	326.9	253.7	1,028.9	870.9
Oncology Systems | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	340.3	310.7	985.7	896.6
Oncology Systems | Americas
Disaggregation of Revenue [Line Items]
Revenues	323.2	286.9	981.8	909.7
Oncology Systems | EMEA
Disaggregation of Revenue [Line Items]
Revenues	208.5	157.6	633.2	494.1
Oncology Systems | APAC
Disaggregation of Revenue [Line Items]
Revenues	135.5	119.9	399.6	363.7
Oncology Systems | North America
Disaggregation of Revenue [Line Items]
Revenues	298.7	274.7	924.6	859.4
Oncology Systems | International
Disaggregation of Revenue [Line Items]
Revenues	368.5	289.7	1,090.0	908.1
Oncology Systems | Hardware
Disaggregation of Revenue [Line Items]
Revenues	276.5	214.9	881.2	736.0
Oncology Systems | Software
Disaggregation of Revenue [Line Items]
Revenues	125.1	110.4	366.9	342.8
Oncology Systems | Service
Disaggregation of Revenue [Line Items]
Revenues	265.6	239.1	766.5	688.7
Varian Particle Therapy
Disaggregation of Revenue [Line Items]
Revenues	41.9	68.4	102.9	130.0
Varian Particle Therapy | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Varian Particle Therapy | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	41.9	68.4	102.9	130.0
Varian Particle Therapy | Americas
Disaggregation of Revenue [Line Items]
Revenues	19.4	49.4	57.7	66.4
Varian Particle Therapy | EMEA
Disaggregation of Revenue [Line Items]
Revenues	21.2	11.9	43.3	44.7
Varian Particle Therapy | APAC
Disaggregation of Revenue [Line Items]
Revenues	1.3	7.1	1.9	18.9
Varian Particle Therapy | North America
Disaggregation of Revenue [Line Items]
Revenues	19.4	49.4	57.7	66.4
Varian Particle Therapy | International
Disaggregation of Revenue [Line Items]
Revenues	22.5	19.0	45.2	63.6
Varian Particle Therapy | Hardware
Disaggregation of Revenue [Line Items]
Revenues	38.1	66.5	95.5	123.4
Varian Particle Therapy | Software
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Varian Particle Therapy | Service
Disaggregation of Revenue [Line Items]
Revenues	$ 3.8	$ 1.9	$ 7.4	$ 6.6