SEGMENT INFORMATION - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 30, 2018	Mar. 31, 2017	Mar. 30, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 729.9	$ 663.2	$ 1,408.4	$ 1,264.7
Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	363.7	334.8	702.0	617.2
Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	366.2	328.4	706.4	647.5
Americas
Disaggregation of Revenue [Line Items]
Revenues	340.2	341.6	696.9	639.8
EMEA
Disaggregation of Revenue [Line Items]
Revenues	253.8	185.3	446.8	369.3
APAC
Disaggregation of Revenue [Line Items]
Revenues	135.9	136.3	264.7	255.6
North America
Disaggregation of Revenue [Line Items]
Revenues	318.6	319.3	664.2	601.7
International
Disaggregation of Revenue [Line Items]
Revenues	411.3	343.9	744.2	663.0
Hardware
Disaggregation of Revenue [Line Items]
Revenues	341.7	314.6	662.1	580.0
Software
Disaggregation of Revenue [Line Items]
Revenues	126.7	118.4	241.8	230.6
Service
Disaggregation of Revenue [Line Items]
Revenues	261.5	230.2	504.5	454.1
Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues	698.0	631.9	1,347.4	1,203.1
Oncology Systems | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	363.7	334.8	702.0	617.2
Oncology Systems | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	334.3	297.1	645.4	585.9
Oncology Systems | Americas
Disaggregation of Revenue [Line Items]
Revenues	321.2	332.0	658.6	622.8
Oncology Systems | EMEA
Disaggregation of Revenue [Line Items]
Revenues	241.2	167.5	424.7	336.5
Oncology Systems | APAC
Disaggregation of Revenue [Line Items]
Revenues	135.6	132.4	264.1	243.8
Oncology Systems | North America
Disaggregation of Revenue [Line Items]
Revenues	299.6	309.7	625.9	584.7
Oncology Systems | International
Disaggregation of Revenue [Line Items]
Revenues	398.4	322.2	721.5	618.4
Oncology Systems | Hardware
Disaggregation of Revenue [Line Items]
Revenues	311.6	284.5	604.7	523.1
Oncology Systems | Software
Disaggregation of Revenue [Line Items]
Revenues	126.7	118.4	241.8	230.6
Oncology Systems | Service
Disaggregation of Revenue [Line Items]
Revenues	259.7	229.0	500.9	449.4
Varian Particle Therapy
Disaggregation of Revenue [Line Items]
Revenues	31.9	31.3	61.0	61.6
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	31.9	31.3	61.0	61.6
Varian Particle Therapy | Americas
Disaggregation of Revenue [Line Items]
Revenues	19.0	9.6	38.3	17.0
Varian Particle Therapy | EMEA
Disaggregation of Revenue [Line Items]
Revenues	12.6	17.8	22.1	32.8
Varian Particle Therapy | APAC
Disaggregation of Revenue [Line Items]
Revenues	0.3	3.9	0.6	11.8
Varian Particle Therapy | North America
Disaggregation of Revenue [Line Items]
Revenues	19.0	9.6	38.3	17.0
Varian Particle Therapy | International
Disaggregation of Revenue [Line Items]
Revenues	12.9	21.7	22.7	44.6
Varian Particle Therapy | Hardware
Disaggregation of Revenue [Line Items]
Revenues	30.1	30.1	57.4	56.9
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	$ 1.8	$ 1.2	$ 3.6	$ 4.7