SEGMENT INFORMATION - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Apr. 03, 2020	Mar. 29, 2019	Apr. 03, 2020	Mar. 29, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 794.5	$ 779.4	$ 1,623.4	$ 1,520.4
Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	394.2	402.6	795.1	769.2
Products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	400.3	376.8	828.3	751.2
Americas
Disaggregation of Revenue [Line Items]
Revenues	387.9	371.3	790.1	721.7
EMEA
Disaggregation of Revenue [Line Items]
Revenues	250.9	261.5	523.8	512.5
APAC
Disaggregation of Revenue [Line Items]
Revenues	155.7	146.6	309.5	286.2
North America
Disaggregation of Revenue [Line Items]
Revenues	362.2	343.4	740.7	672.1
International
Disaggregation of Revenue [Line Items]
Revenues	432.3	436.0	882.7	848.3
Hardware
Disaggregation of Revenue [Line Items]
Revenues	340.9	367.0	699.9	714.2
Software
Disaggregation of Revenue [Line Items]
Revenues	154.7	144.2	303.5	275.4
Service
Disaggregation of Revenue [Line Items]
Revenues	298.9	268.2	620.0	530.8
Oncology Systems | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	381.0	402.6	763.0	769.2
Oncology Systems | Products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	379.5	344.2	779.9	680.1
Oncology Systems | Americas
Disaggregation of Revenue [Line Items]
Revenues	369.7	357.1	748.6	687.9
Oncology Systems | EMEA
Disaggregation of Revenue [Line Items]
Revenues	240.9	245.3	500.7	479.8
Oncology Systems | APAC
Disaggregation of Revenue [Line Items]
Revenues	149.9	144.4	293.6	281.6
Oncology Systems | North America
Disaggregation of Revenue [Line Items]
Revenues	343.9	329.2	699.2	638.3
Oncology Systems | International
Disaggregation of Revenue [Line Items]
Revenues	416.6	417.6	843.7	811.0
Oncology Systems | Hardware
Disaggregation of Revenue [Line Items]
Revenues	316.1	339.1	636.1	652.7
Oncology Systems | Software
Disaggregation of Revenue [Line Items]
Revenues	153.2	144.2	302.0	275.4
Oncology Systems | Service
Disaggregation of Revenue [Line Items]
Revenues	291.2	263.5	604.8	521.2
Proton Solutions | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	1.5	0.0	1.5	0.0
Proton Solutions | Products and services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	20.8	32.6	48.4	71.1
Proton Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	11.4	14.2	28.3	33.8
Proton Solutions | EMEA
Disaggregation of Revenue [Line Items]
Revenues	9.8	16.2	20.1	32.7
Proton Solutions | APAC
Disaggregation of Revenue [Line Items]
Revenues	1.1	2.2	1.5	4.6
Proton Solutions | North America
Disaggregation of Revenue [Line Items]
Revenues	11.5	14.2	28.3	33.8
Proton Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	10.8	18.4	21.6	37.3
Proton Solutions | Hardware
Disaggregation of Revenue [Line Items]
Revenues	13.1	27.9	33.2	61.5
Proton Solutions | Software
Disaggregation of Revenue [Line Items]
Revenues	1.5	0.0	1.5	0.0
Proton Solutions | Service
Disaggregation of Revenue [Line Items]
Revenues	7.7	4.7	15.2	9.6
Other | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	11.7	0.0	30.6	0.0
Other | Americas
Disaggregation of Revenue [Line Items]
Revenues	6.8	0.0	13.2	0.0
Other | EMEA
Disaggregation of Revenue [Line Items]
Revenues	0.2	0.0	3.0	0.0
Other | APAC
Disaggregation of Revenue [Line Items]
Revenues	4.7	0.0	14.4	0.0
Other | North America
Disaggregation of Revenue [Line Items]
Revenues	6.8	0.0	13.2	0.0
Other | International
Disaggregation of Revenue [Line Items]
Revenues	4.9	0.0	17.4	0.0
Other | Hardware
Disaggregation of Revenue [Line Items]
Revenues	$ 11.7	$ 0.0	$ 30.6	$ 0.0