SEGMENT INFORMATION - Operating Results Information for Each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Apr. 01, 2016	Mar. 31, 2017	Apr. 01, 2016
Segment Reporting Information [Line Items]
Revenues	$ 655.0	$ 615.2	$ 1,266.8	$ 1,231.0
Operating Earnings (Loss)	89.8	103.0	115.9	191.3
Unallocated corporate
Segment Reporting Information [Line Items]
Operating Earnings (Loss)	(13.0)	(7.7)	(61.4)	(13.5)
Operating Segments
Segment Reporting Information [Line Items]
Revenues	655.0	615.1	1,266.8	1,230.9
Operating Earnings (Loss)	102.8	111.8	177.3	207.3
Operating Segments | Oncology Systems
Segment Reporting Information [Line Items]
Revenues	623.7	584.2	1,205.2	1,173.6
Operating Earnings (Loss)	122.6	124.0	247.4	231.5
Operating Segments | Varian Particle Therapy
Segment Reporting Information [Line Items]
Revenues	31.3	30.9	61.6	57.3
Operating Earnings (Loss)	(19.8)	(12.2)	(70.1)	(24.2)
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	0.0	0.1	0.0	0.1
Operating Earnings (Loss)	$ 0.0	$ (1.1)	$ 0.0	$ (2.5)