Segment Information - Disaggregation of Revenue (Details) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 28, 2018 USD ($)	Jun. 29, 2018 USD ($)	Mar. 30, 2018 USD ($)	Dec. 29, 2017 USD ($)	Sep. 29, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 30, 2016 USD ($)	Sep. 28, 2018 USD ($) segment	Sep. 29, 2017 USD ($)	Sep. 30, 2016 USD ($)
Disaggregation of Revenue [Line Items]
Number of reportable segments | segment									2
Revenues	$ 801.6	$ 709.1	$ 729.9	$ 678.5	$ 721.8	$ 632.8	$ 663.2	$ 601.5	$ 2,919.1	$ 2,619.3	$ 2,593.7
Revenues, net of prior business											2,593.2
Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									2,770.2	2,436.8	2,430.6
Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									148.9	182.5	162.6
Hardware
Disaggregation of Revenue [Line Items]
Revenues									1,366.6	1,211.9	1,222.9
Hardware | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									1,231.5	1,039.4	1,069.8
Hardware | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									135.1	172.5	153.1
Software
Disaggregation of Revenue [Line Items]
Revenues									499.2	462.9	476.1
Software | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									495.4	462.9	476.1
Software | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									3.8	0.0	0.0
Service
Disaggregation of Revenue [Line Items]
Revenues									1,053.3	944.5	894.2
Service | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									1,043.3	934.5	884.7
Service | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									10.0	10.0	9.5
Prior Business | Hardware
Disaggregation of Revenue [Line Items]
Revenues											0.5
Americas
Disaggregation of Revenue [Line Items]
Revenues									1,436.9	1,344.6	1,288.7
Americas | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									1,351.3	1,256.8	1,233.7
Americas | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									85.6	87.8	55.0
Americas | Prior Business
Disaggregation of Revenue [Line Items]
Revenues											0.5
EMEA
Disaggregation of Revenue [Line Items]
Revenues									942.8	759.2	798.1
EMEA | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									883.2	691.1	712.7
EMEA | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									59.6	68.1	85.4
Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues									539.4	515.5	506.4
Asia Pacific | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									535.7	488.9	484.2
Asia Pacific | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									3.7	26.6	22.2
North America
Disaggregation of Revenue [Line Items]
Revenues									1,347.2	1,267.8	1,205.4
North America | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									1,261.6	1,180.0	1,150.4
North America | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									85.6	87.8	55.0
International
Disaggregation of Revenue [Line Items]
Revenues									1,571.9	1,351.5	1,387.8
International | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									1,508.6	1,256.8	1,280.2
International | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									63.3	94.7	107.6
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenues									1,434.8	1,221.5	1,282.4
Transferred at Point in Time | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									1,431.0	1,221.5	1,282.4
Transferred at Point in Time | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									3.8	0.0	0.0
Transferred at Point in Time | Prior Business
Disaggregation of Revenue [Line Items]
Revenues											0.5
Transferred over Time
Disaggregation of Revenue [Line Items]
Revenues									1,484.3	1,397.8	1,310.8
Transferred over Time | Oncology Systems
Disaggregation of Revenue [Line Items]
Revenues									1,339.2	1,215.3	1,148.2
Transferred over Time | Proton Solutions
Disaggregation of Revenue [Line Items]
Revenues									$ 145.1	$ 182.5	$ 162.6