SEGMENT INFORMATION - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 28, 2019	Jun. 29, 2018	Jun. 28, 2019	Jun. 29, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 825.8	$ 709.1	$ 2,346.2	$ 2,117.5
Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	437.1	326.9	1,206.3	1,028.9
Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	388.7	382.2	1,139.9	1,088.6
Americas
Disaggregation of Revenue [Line Items]
Revenues	401.2	342.6	1,122.9	1,039.5
EMEA
Disaggregation of Revenue [Line Items]
Revenues	271.3	229.7	783.8	676.5
APAC
Disaggregation of Revenue [Line Items]
Revenues	153.3	136.8	439.5	401.5
North America
Disaggregation of Revenue [Line Items]
Revenues	378.7	318.1	1,050.8	982.3
International
Disaggregation of Revenue [Line Items]
Revenues	447.1	391.0	1,295.4	1,135.2
Hardware
Disaggregation of Revenue [Line Items]
Revenues	387.9	314.6	1,102.1	976.7
Software
Disaggregation of Revenue [Line Items]
Revenues	155.7	125.1	431.1	366.9
Service
Disaggregation of Revenue [Line Items]
Revenues	282.2	269.4	813.0	773.9
Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues	792.9	667.2	2,242.2	2,014.6
Oncology Systems | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	433.8	326.9	1,203.0	1,028.9
Oncology Systems | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	359.1	340.3	1,039.2	985.7
Oncology Systems | Americas
Disaggregation of Revenue [Line Items]
Revenues	385.6	323.2	1,073.5	981.8
Oncology Systems | EMEA
Disaggregation of Revenue [Line Items]
Revenues	256.4	208.5	736.2	633.2
Oncology Systems | APAC
Disaggregation of Revenue [Line Items]
Revenues	150.9	135.5	432.5	399.6
Oncology Systems | North America
Disaggregation of Revenue [Line Items]
Revenues	363.1	298.7	1,001.4	924.6
Oncology Systems | International
Disaggregation of Revenue [Line Items]
Revenues	429.8	368.5	1,240.8	1,090.0
Oncology Systems | Hardware
Disaggregation of Revenue [Line Items]
Revenues	361.7	276.5	1,014.4	881.2
Oncology Systems | Software
Disaggregation of Revenue [Line Items]
Revenues	154.4	125.1	429.8	366.9
Oncology Systems | Service
Disaggregation of Revenue [Line Items]
Revenues	276.8	265.6	798.0	766.5
Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues	30.9	41.9	102.0	102.9
Proton Solutions | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	1.3	0.0	1.3	0.0
Proton Solutions | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	29.6	41.9	100.7	102.9
Proton Solutions | Americas
Disaggregation of Revenue [Line Items]
Revenues	14.8	19.4	48.6	57.7
Proton Solutions | EMEA
Disaggregation of Revenue [Line Items]
Revenues	14.9	21.2	47.6	43.3
Proton Solutions | APAC
Disaggregation of Revenue [Line Items]
Revenues	1.2	1.3	5.8	1.9
Proton Solutions | North America
Disaggregation of Revenue [Line Items]
Revenues	14.8	19.4	48.6	57.7
Proton Solutions | International
Disaggregation of Revenue [Line Items]
Revenues	16.1	22.5	53.4	45.2
Proton Solutions | Hardware
Disaggregation of Revenue [Line Items]
Revenues	24.2	38.1	85.7	95.5
Proton Solutions | Software
Disaggregation of Revenue [Line Items]
Revenues	1.3	0.0	1.3	0.0
Proton Solutions | Service
Disaggregation of Revenue [Line Items]
Revenues	5.4	$ 3.8	15.0	$ 7.4
Other
Disaggregation of Revenue [Line Items]
Revenues	2.0		2.0
Other | Products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	2.0		2.0
Other | Products and Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	0.0		0.0
Other | Americas
Disaggregation of Revenue [Line Items]
Revenues	0.8		0.8
Other | EMEA
Disaggregation of Revenue [Line Items]
Revenues	0.0		0.0
Other | APAC
Disaggregation of Revenue [Line Items]
Revenues	1.2		1.2
Other | North America
Disaggregation of Revenue [Line Items]
Revenues	0.8		0.8
Other | International
Disaggregation of Revenue [Line Items]
Revenues	1.2		1.2
Other | Hardware
Disaggregation of Revenue [Line Items]
Revenues	2.0		2.0
Other | Software
Disaggregation of Revenue [Line Items]
Revenues	0.0		0.0
Other | Service
Disaggregation of Revenue [Line Items]
Revenues	$ 0.0		$ 0.0