SEGMENT INFORMATION - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 29, 2019	Mar. 30, 2018	Mar. 29, 2019	Mar. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 779.4	$ 729.9	$ 1,520.4	$ 1,408.4
Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	402.6	363.7	769.2	702.0
Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	376.8	366.2	751.2	706.4
Americas
Disaggregation of Revenue [Line Items]
Revenues	371.3	340.2	721.7	696.9
EMEA
Disaggregation of Revenue [Line Items]
Revenues	261.5	253.8	512.5	446.8
APAC
Disaggregation of Revenue [Line Items]
Revenues	146.6	135.9	286.2	264.7
North America
Disaggregation of Revenue [Line Items]
Revenues	343.4	318.6	672.1	664.2
International
Disaggregation of Revenue [Line Items]
Revenues	436.0	411.3	848.3	744.2
Hardware
Disaggregation of Revenue [Line Items]
Revenues	367.0	341.7	714.2	662.1
Software
Disaggregation of Revenue [Line Items]
Revenues	144.2	126.7	275.4	241.8
Service
Disaggregation of Revenue [Line Items]
Revenues	268.2	261.5	530.8	504.5
Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues	746.8	698.0	1,449.3	1,347.4
Oncology Systems | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	402.6	363.7	769.2	702.0
Oncology Systems | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	344.2	334.3	680.1	645.4
Oncology Systems | Americas
Disaggregation of Revenue [Line Items]
Revenues	357.1	321.2	687.9	658.6
Oncology Systems | EMEA
Disaggregation of Revenue [Line Items]
Revenues	245.3	241.2	479.8	424.7
Oncology Systems | APAC
Disaggregation of Revenue [Line Items]
Revenues	144.4	135.6	281.6	264.1
Oncology Systems | North America
Disaggregation of Revenue [Line Items]
Revenues	329.2	299.6	638.3	625.9
Oncology Systems | International
Disaggregation of Revenue [Line Items]
Revenues	417.6	398.4	811.0	721.5
Oncology Systems | Hardware
Disaggregation of Revenue [Line Items]
Revenues	339.1	311.6	652.7	604.7
Oncology Systems | Software
Disaggregation of Revenue [Line Items]
Revenues	144.2	126.7	275.4	241.8
Oncology Systems | Service
Disaggregation of Revenue [Line Items]
Revenues	263.5	259.7	521.2	500.9
Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues	32.6	31.9	71.1	61.0
Proton Solutions | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Proton Solutions | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	32.6	31.9	71.1	61.0
Proton Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	14.2	19.0	33.8	38.3
Proton Solutions | EMEA
Disaggregation of Revenue [Line Items]
Revenues	16.2	12.6	32.7	22.1
Proton Solutions | APAC
Disaggregation of Revenue [Line Items]
Revenues	2.2	0.3	4.6	0.6
Proton Solutions | North America
Disaggregation of Revenue [Line Items]
Revenues	14.2	19.0	33.8	38.3
Proton Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	18.4	12.9	37.3	22.7
Proton Solutions | Hardware
Disaggregation of Revenue [Line Items]
Revenues	27.9	30.1	61.5	57.4
Proton Solutions | Software
Disaggregation of Revenue [Line Items]
Revenues	0.0	0.0	0.0	0.0
Proton Solutions | Service
Disaggregation of Revenue [Line Items]
Revenues	$ 4.7	$ 1.8	$ 9.6	$ 3.6